# 7. DISPLAY MODES

A "display mode" consists primarily of an algorithm that Elvis uses internally to convert the bytes in a buffer into an image in a window. The same algorithm is also used for printing via the ":lpr" command.

The display mode also affects tag lookup, and image-dependent operations such as determining the column number of the cursor's location, and moving the cursor vertically.

You can list the supported display modes by giving the ":display" command without any arguments. Typically, the supported modes will include the following:

    .--------.----------------------------------------------.
    |  MODE  | DESCRIPTION                                  |
    |--------|----------------------------------------------|
    | normal | Traditional vi, displays plain ASCII         |
    | syntax | Like "normal" but does syntax coloring       |
    | hex    | Interactive hex dump, good for binary files  |
    | html   | Simple Web page formatter                    |
    | man    | Simple Man page formatter, like "nroff -man" |
    | tex    | Simple subset of the TeX formatter           |
    ^--------^----------------------------------------------^

Elvis 2.x allows each window to be in a different display mode. You can manually change a window's display mode via the ":display mode" command, where mode is the name of a supported display mode. There is also a ":no" command, which is short for ":display normal".

## 7.1 Options

There are two options which pertain to display modes: display and bufdisplay.

The display option is associated with a window. It always contains the name of the window's current display mode. You aren't allowed to change the value of this option directly; you must use the ":display mode" command to change the display mode. This option exists solely so that you can write EX scripts which behave differently, depending on the display mode.

The bufdisplay option is associated with a buffer. It should be set to the name of the usual display mode for that buffer. Typically this option will be set from the elvis.arf initialization file, based on the name of the file like this:

    	let e=tolower(dirext(filename))
    	if knownsyntax(filename)
    	then set! bufdisplay=syntax
    	else if os=="unix" && buflines >= 1
    	then 1s/^#! *[^ ]*\/\([^ ]\+\).*/set! bufdisplay="syntax \1"/x
    	if e<<4==".htm"
    	then set! bufdisplay=html
    	if e==".man" || e==".1"
    	then set! bufdisplay=man
    	if binary
    	then set! bufdisplay=hex

When a new window is created for that buffer, or an existing window switches to that buffer, that window's display mode will automatically be switched to the bufdisplay mode.

The bufdisplay mode also affects the ^Wd visual command. This command toggles the window between the normal mode and the bufdisplay mode. If bufdisplay is also set to "normal", then `^Wd` will toggle between the normal and hex display modes.

## 7.2 Normal mode

The "normal" display mode looks like a traditional vi screen. All characters are displayed literally except for the following...

Tab
  The tab character is displayed as a variable number of spaces -- however many are needed to move to the next tabstop position.
Newline
  The newline character (linefeed) marks the end of a line.
Other control characters
  Control characters other than tab and newline are displayed as a caret and a printable ASCII character. For example Control-A is displayed as ^A, and NUL is displayed as ^@. The delete character is displayed as ^?.
Non-ASCII characters
  The appearance of non-ASCII characters (i.e., characters 128-255) is controlled by the nonascii option. By default, most non-ASCII characters are assumed to be ordinary printable characters.

## 7.3 Syntax mode

The "syntax" display mode acts exactly like the normal mode, except that this mode automatically uses different faces for various types of tokens in any supported programming language. You can then use the :color command to assign colors and other attributes for each face.

### 7.3.1 Language specification

All supported languages are described in a file named "elvis.syn". Each time a window switches to the "syntax" display mode, Elvis scans this file for a description of the language. If it can't find a description of the language, then nothing will be displayed in a different face; "syntax" mode will look exactly like "normal" text.

The "elvis.syn" file is a text file. In it, blank lines and lines which start with a '#' are ignored. Other lines begin with the name of an attribute; the remaining words in the line are values for that attribute. Each language's description begins with an attribute named "language". The following lines (up to the next "language" line or the end of the file) describe that language.

The attributes names are:

language
  This word is followed by a whitespace-delimited list of language names. The names are case-sensitive, so you should probably give all names in lowercase so they're easier for the user to type in. The user can indicate which language to use by appending its name to the name of the "syntax" display mode. For example, ":display syntax c++" causes Elvis to highlight the text appropriately for C++.
extension
  This word is followed by the filename extensions which are commonly used for this language. If the user doesn't specify which language to load, then Elvis scans through "elvis.syn" for an extension line which matches the current file name. The extension lines must come immediately after the language line.

  NOTE: Lowercase extensions are compared to filenames in a case-insensitive way. Uppercase extensions will only match uppercase filenames. For example "extension .C" will match "foo.C" but not "bar.c". To avoid ambiguity, any language with an uppercase extension should appear before any language with a similar lowercase extension. To the best of my knowledge, this basically means C++ should be listed before C; and all other languages should simply be listed with lowercase extensions.

foreign
  This word is followed by any extra filename extensions which this language can call. For example, the C++ description includes "`foreign .c`" since C++ can call C functions. This is used by the taglibrary option.
keyword
  This word is followed by a list of words which should be shown in the `keyword` face. If omitted, then no words are shown in the `keyword` face. Long lists can be split into several keyword lines, if you wish. Elvis doesn't care about the order of the words, but the list will be easier to maintain if you keep it alphabetized.

  Elvis supports three forms of keywords...

  - Most keywords begin with an alphanumeric character or a character in the startword list, and continue with zero or more characters which are alphanumeric or in the inword list.
  - The same startword/inword type of keywords can be made somewhat context sensitive by appending a single character which does not appear in the inword. The keyword will only be recognized when it is immediately followed by that character. The HTML syntax highlighting uses this feature to display parameters in a distinctive font.
  - Rarely, you may find it convenient to have keywords which consist of one or two punctuation characters, but which don't match the first form of keywords. This is mostly so that Perl's `$#` variable won't be displayed as a simple dollar sign followed by a comment.

  You can list the same keyword in multiple lines (once each in a keyword line, a font line, an anchor line, and a comment line) to specify the various attributes of each keyword. You don't need to list it in a keyword line first; you can introduce new keywords in any of these four line types.

font
  This word can be used to cause certain keywords to be displayed in some font other than the `keyword` face. The first word after `font` should be the name of the font. The font can be any name you choose, but see the description of the :color command for a list of common names. The line's remaining words are keywords which will be displayed in that font.
color
  This allows you to define a default appearance for fonts that you used in a font line. The syntax is the same as that of the :color command; the only difference is that `color` lines here will never alter values that were configured via real `:color` commands. (This rule allows people to share syntax descriptions while while maintaining separate color preferences.)
anchor
  This offers a way to restrict certain keywords, so they will only be recognized as such if they occur in a particular column. The first word after "anchor" is a column number -- 1 for the leftmost column, 9 for the first tabstop, and so on. You can also use ^ instead of a number to indicate that the keyword can only appear at the front of a line (after optional whitespace but no printed characters). The remainder of the "anchor" line is the list of keywords which are only special when they occur in that column.

  If the column number is prefixed by ~ then the keyword gets preference to another keyword defined with the same column number. This is useful for comment keywords which are subsets or supersets of each other, because the shorter comment keyword will always win else. With ~ the longer one will be considered first.

prefix
  This defines keywords which should be recognized even if they are immediately followed by alphanumeric text. The following alphanumeric text would then be parsed as a separate word, which may be another keyword or some other type of word.

  For example, the syntax description for man-page source code lists `\fB` as a prefix keyword, so `\fBbold\fR` can be parsed correctly.

comment
  This word is followed by a keyword which marks the beginning of a comment. The comment is assumed to end at the end of the line. Comments are normally shown in the `comment` face, but if you've overridden the keyword's font via a font line in `elvis.syn`, then the whole comment will be displayed in that font instead. You can define multiple comment keywords, and assign different fonts to them if you wish.

  The `comment` word can also be followed by a pair of one- or two-character sequences which mark the beginning and end of comments which can include newlines. Elvis only supports one multi-line comment style for each language, and it will always be displayed in the `comment` face.

set
  This is useful for setting options to language-dependent values. It offers a convenient way to set the ccprg and hlobject options, for example. The words after "set" should look like arguments to the :set command.

  WARNING: If you use an `elvis.syn` file which is writable by the public, this could be a security hole. A malicious person could alter it to set ccprg (or even shell) to a value which runs any program they wish.

operator
  This word is followed by a keyword which the language uses as a prefix for operators, and then by a list of characters which can appear in the operator itself. This affects the ^] visual command for tag searches. Presently, the only language that uses this is C++, where it is specified like this:

      operator operator ~!%^&*+|-=[]<>/

preprocessor
  This word is followed by a single character which, when used at the beginning of a line, marks the start of a preprocessor directive. For C, this is the # character. All preprocessor directives will then be shown in the `prep` face. If omitted, nothing is displayed in the `prep` face.
prepquote
  This word is followed by a single character, or a pair of single characters, which are used as the quote characters surrounding a file name in a preprocessor directive. For C, this is the < and > characters. The name of the included file will then be displayed using the `string` face. If omitted, then preprocessor file names will be highlighted as though they were ordinary expressions.
function
  This word is followed by a single character which, if it appears after a word, indicates that the word should be displayed in the `function` face. For most languages, this will be a '(' character. If omitted, nothing is displayed in the `function` face and the smartargs option won't work.
startword
inword
  These can be followed by a list of punctuation characters which may appear at the start of a word, or in the remainder of the word, respectively. Letters and digits are always legal in words; you don't need to list them.
other
  This word indicates which types of words should be displayed in the `other` face. If omitted, nothing is displayed in the `other` face. It can be any combination of the following symbols:

      .-------------.-------------------------------------------------.
      | SYMBOL      | HOW TO RECOGNIZE "OTHER" WORDS                  |
      |-------------|-------------------------------------------------|
      | allcaps     | length >= 2 chars, no lowercase characters      |
      | initialcaps | 1st character is uppercase, some are lowercase  |
      | initialpunct| 1st character is punctuation, from "startword"  |
      | mixedcaps   | 1st character is lowercase, some are uppercase  |
      | final_t     | length >= 3 chars, ends with "_t"               |
      ^-------------^-------------------------------------------------^

mostly
  Words that aren't keywords, functions, or other special words, are generally considered to be variables. By default, they're displayed in the "variable" face, but you can use the `mostly` line to specify some other face to use. For example, HTML's syntax description uses "`mostly normal`" so that plain text will be displayed as "normal" text. This is important because ":set spell" normally performs spell checking on "normal" text, but not "variable" names.
backslash
  This defines the character that is used for quoting delimiters in a string, character, or regexp literal. The default is "\", the backslash character. You can use a `backslash` line to define some other punctuation character to use as the quoting character, or say "`backslash none`" to disable this type of quoting.
string
  This word is followed by a single character, or a pair of single characters, which are used as the quote characters surrounding string literals. For C, this is the " character. String literals will then be displayed using the `string` face. If omitted, then strings will not be recognized.

  Elvis allows you to define two forms of strings. Each form should be defined on a separate string line.

strnewline
  This is followed by backslash, allowed, indent, or empty to indicate how strings can be continued across lines. The default is backslash which indicates a C-style backslash is required to quote the newline characters (which C will then exclude from the string, but Elvis doesn't care about that). The other values all indicate that a backslash is not needed, and also give some hints that help Elvis detect whether the top of the screen is inside a multi-line string. Specifically, the indent value means that indented lines rarely occur in a continuation of a string, empty means that empty lines are probably not part of a string, and allowed makes no promises.

  The allowed value would be too slow if strings' opening and closing quotes are identical (e.g., if the " character appears at both ends of a string); in this situation, Elvis uses empty instead.

  Note that the hints are only used for detecting whether the first line starts in a multi-line string. When drawing text after that, Elvis treats all non-backslash values identically.

character
  This word is followed by a single character, or a pair of single characters, which are used as the quote characters surrounding character literals. For C, this is the ' character. This is shown using the `char` face. Character literals are not allowed to span lines.
regexp
  This word is followed by a list of characters which can be used for delimiting a regular expression, which some languages support as a means for specifying strings with metacharacters. (See Section 5 of this manual for a description of Elvis' own implementation of regular expressions, which is a typical example.) Regular expressions are displayed using the `regexp` face.

  Note that `regexp` accepts a list of characters, while `string` and `character` support only a single character. This is because many programming languages allow the programmer to choose from a variety of delimiting characters.

useregexp
  The most commonly used delimiter for regular expressions is '/', which many languages also use as the division operator. To avoid mistakenly displaying the division operator as the start of a regular expression, Elvis must be sensitive to the context in which it is used. That's what this word is for. The `useregexp` word is followed by a list of keywords and/or punctuation characters which allow the next character to be recognized as a regular expression. Additionally, regular expressions are allowed at the start of a line.
useregsub
  This is used for listing keywords and punctuation characters which may be followed by a regular expression and then substitution text.
ignorecase
  This word should be followed by true or false. If true, then Elvis won't distinguish between uppercase and lowercase letters when testing whether a word is a keyword (except that in the elvis.syn file, the keywords should be listed in lowercase). If omitted, Elvis assumes it should be false.

  NOTE: When using "`ignorecase true`", you must give all keywords in lowercase. The "`ignorecase true`" behavior is implemented by converting each word in your text file to lowercase before looking it up to see if it is a keyword, so if your keywords aren't in lowercase then they will never be recognized.

documentation
  This word should be followed by a magic character sequence which marks the end of embedded documentation in a source file, if the language supports it. The embedded documentation is assumed to start on any other line which begins with the same character as the end word.

  Basically, this is intended to support Perl's POD text, though I hope it is more versatile than that. Perl's syntax description includes "`documentation =cut`" which causes "=cut" to mark the end of embedded POD text, and any other line that starts with "=" to mark the beginning or continuation of POD text.

  Markup lines (those that start with "=" for Perl) are drawn in the "`docmarkup`" face. Indented lines are drawn in the "`docindent`" face, and all other documentation lines are drawn in the "`doc`" face. You can use the :color command to change the appearance of the text, and :check to define the spell-checking rules.

### 7.3.2 Example

The elvis.syn file shipped with Elvis contains some good examples of language descriptions. Here's an excerpt from it, describing the Java language.

    language java
    extension .java .jav
    keyword abstract boolean break byte byvalue case cast catch char
    keyword class const continue default do double else extends false
    keyword final finally float for future generic goto if implements
    keyword import inner instanceof int interface long native new null
    keyword operator outer package private protected public rest return
    keyword short static super switch synchronized this throw throws
    keyword transient true try var void volatile while
    comment	//
    comment /* */
    function (
    string "
    character '
    startword _
    inword _
    other allcaps initialcaps

There is no preprocessor line, because java doesn't use a preprocessor. The "allcaps" and "initialcaps" symbols are given so that constants and class names will be shown in the `other` face.

## 7.4 Hex mode

The "hex" display mode is an interactive hex dump of the buffer. This is good for examining or editing binary files.

One handy feature is the ability to enter characters in hex (either in input mode or as the argument to an r visual command) by typing `^X` followed by two hex digits. In input mode, you can also type `^X^X` followed by many hex digits to enter multiple bytes; a single `^X` ends hex input. This feature is always available regardless of the display mode... but this is where is it most useful.

## 7.5 HTML mode

HTML is the language used for constructing pages on the World Wide Web. Elvis' "html" display mode supports a subset of HTML, which it uses for displaying the online help documentation (including this very document).

HTML is a markup language. This means that documents contain a mixture of text and formatting instructions. In HTML there are two types of instructions, called tags and entities. When the document is processed by a program such as Netscape or Elvis (in html mode), the tags are stripped out, the entities are converted to a kind of text, and the text is formatted and presented to the user. Ordinarily the user will never see the tags.

Since Elvis is primarily an editor, not a viewer, it has two options which allow the tags to become visible: the showmarkups option causes a tag to become visible if the cursor is moved onto it, and the list option makes all tags visible regardless of the cursor position.

There are a lot of good "How To Use HTML" documents on the Net. This is not one of them! I don't intend to do much more than describe the quirks of Elvis' implementation of HTML here.

I added HTML support to Elvis mostly to support the online help. Consequently, if a feature is hard to implement and the online documentation doesn't use it, then I didn't implement that feature.

If you intend to use Elvis as a browser, then I suggest you read the appropriate section in the Tip chapter.

### 7.5.1 Formatting tags

Elvis supports the following HTML tags. Unsupported tags are silently ignored. Newline characters aren't supported within tags; each tag must fit on a single line.

<html> ... </html>
  The entire document should be enclosed in these tags. They don't actually do anything to help format the document, but they may help programs recognize that the document is, in fact, written in HTML.
<head> ... </head>
  These should be used to bracket the document's header, if it has one.
<title> ... </title>
  These tags are only legal in the document's header. Any text between the <title> and </title> tags will be stored internally as the title of the document. If you print the document, Elvis will display the title at the top of each page.
<body> ... </body>
  These should be used to bracket the body of the document. They don't actually do anything in Elvis, but real Web browsers such as Netscape allow you to specify backgrounds and patterns via BGCOLOR=... and BACKGROUND=... arguments, respectively.
<h1> ... </h1>
  These tags bracket the most visible type of section header. Elvis displays <h1> ... </h1> headers in boldface, flush against the left edge of the page. When printing, these headers cause a page break.
<h2> ... </h2>
  These bracket the second most visible type of section header. Elvis displays <h2> ... </h2> headers in boldface, indented slightly from the left edge. When printing, these may cause a page break if they would otherwise appear near the bottom of a page.
<h3> ... </h3>
  These bracket the third most visible type of section header. Elvis displays them in boldface, indented fully from the left edge so that it lines up with normal text.
<h4>...</h4>
<h5>...</h5>
<h6>...</h6>
  These are very minor section headers. Conventional wisdom says that if you're using this many section headers then you would probably do better to split your document into several smaller documents. Elvis displays these headers in an italic font.
<p align=...>
  This tag should be placed at the start of each normal paragraph, with the possible exception of the first paragraph after a section header. It causes a blank line to be generated, and any later text to appear starting on a new line.

  Elvis ignores the `align=` parameter. Real browsers use this to set the horizontal alignment to `left`, `right`, or `center`.

<br>
  This causes any later text to appear starting on a new line. It differs from <p> in that <br> doesn't output a blank line.
<hr size=... width=...>
  This outputs a "horizontal rule" -- a line all the way across the page.

  Elvis ignores the `size=` and `width=` parameters. They specify the thickness and width of the line, respectively.

<img alt=... src=...>
  Elvis can't display graphics, but if it encounters an <img> tag which has an alternate text form (as denoted by an alt="text" parameter) then it'll display the alternate text. Otherwise Elvis will display "src" URL. Also, if the image isn't already part of a hypertext link, then Elvis will treat it as a link to the image's binary data; this offers you a way to fetch images, even though Elvis can't display them. The supported URL formats are described in the discussion of the <a> tag, below.
<frame name=... src=...>
  Elvis can't display frames either, but it will display the frame's name, and treat that name as a hypertext link to the frame's document. This offers a simple work-around for Elvis' lack of real frame support. The supported URL formats are described in the discussion of the <a> tag, below.
<blockquote> ... </blockquote>
  This is used to mark a large chunk text which is quoted from another source. Elvis will indent the enclosed text.
<pre graphic> ... </pre>
  This brackets text which has already been preformatted by the document's author. Elvis will treat tabs and newlines literally. (Outside of <pre> ... </pre>, they would normally be treated like spaces.) This has been used for presenting tables, poetry, and source code examples.

  The optional `graphic` parameter is a non-standard Elvis extension. If you start with <pre graphic> then Elvis will convert certain characters into graphic line-drawing characters. When adjacent to a hyphen character, the hyphen, period, caret are converted into appropriate graphic characters. Additionally, the vertical bar character is always converted to a graphic character. The following was done with a plain <pre>...

      .--.--.
      |--|--|
      |  |  |
      ^--^--^

  ... and this was done with <pre graphic>...

      .--.--.
      |--|--|
      |  |  |
      ^--^--^

<table background=... bgcolor=... border=...> ... </table>
<tr>...</tr>
<th align=... valign=...> ... </th>
<td align=... valign=...> ... </td>
  These are used for implementing tables in HTML 3.0. Each table should be enclosed in a <table>...</table> pair. Within the table, each row should be delimited with a <tr>...</tr> pair. Within each row, the information for each column should be enclosed in either a <th>...</th> pair for headers, or a <td>...</td> pair for data.

  Elvis doesn't really support these tags very well. Only the bare essentials of these commands have been implemented. They are intended to make tables recognizable as being tables, but not necessarily make them easy to read.

<dir>...</dir>
<xmp>...</xmp>
  These are treated almost exactly like <pre> ... </pre>. There are supposed to be some differences, but Elvis doesn't support those differences.
<dl compact> ... </dl>
  These are used to bracket a list of definitions. The definitions themselves are marked with the <dt> and <dd> tags, described below.

  Elvis ignores the optional `compact` parameter.

<dt>
  The text after this tag is used as a term to be defined. Elvis displays this text in bold face, indented by the same amount as normal text. This is only legal in a <dl>...</dl> pair.

  It seems that most web browsers display the terms in the normal font, not bold face like Elvis. You might want to wrap the term in <strong>...</strong> tags to make it look better in a browser.

<dd>
  The text after this tag is used as the definition of a term. Elvis displays it in the normal font, indented somewhat more than normal text or the <dt> text. This is only legal in a <dl>...</dl> pair.
<ol> ... </ol>
  These are used to enclose an ordered list. The official specifications say that lists may be nested inside one another, but Elvis doesn't allow ordered lists to appear inside any other type of list. If a document uses <ol> ... </ol> inside another list, then Elvis will act as though <ul> ... </ul> had been used instead. This means that the list items will be marked with bullets instead of numbers. Within the list, <li> tags are used to mark the items.
<ul> ... </ul>
  These enclose an unordered list. Each item in the list should be marked with a <li> tag.
<menu> ... </menu>
  These enclose an unordered list, like <ul> ... </ul>, but other Web browsers may display <menu> ... </menu> lists in a more compact manner.
<li>
  This is used to mark the start of a new item in a list.
<input type=... size=... value=...>
<textarea cols=...>
  Elvis can display a mockup of a form, so you can have some idea of how the form would look on a real browser. The forms won't really work in Elvis! Elvis displays forms for the sole purpose of helping you define the form layout. You can use the :color command to define the appearance of the form elements; their faces all have names that start with "`form_`". The <textarea> image is always 3 rows high, regardless of any rows=... value you supply.
<a href=... target=... title=...> </a>
<a name=...> </a>
  There are two forms of this tag: <a href=URL>...</a> to mark the source of a hypertext link, and <a name=anchor></a> to mark the destination of a hypertext link.

  Elvis doesn't actually do anything with the `target=` and `title=` parameters. In a real browser, `target=` identifies the frame into which the URL should be loaded, and `title=` gives human-readable text, usually shown as a "tool tip" when the cursor is hovering on the link.

  Elvis doesn't support as many URL protocols as a real browser. It only supports the pseudo-protocol "buffer:", and the real protocols "file:" and (on some platforms) "http:" and "ftp:". (However, Elvis can be configured to support extra protocols.) Only the following URL formats are supported:

      	buffer:bufname
      		Switch to the buffer named bufname.  Within that
      		buffer, the cursor will be moved to the position
      		of the most recent activity to that buffer.  This
      		is an Elvis-only extension!

      	[protocol:]filename.ext
      		Load the named file, and move the cursor to the
      		top of that file's buffer.

      	[protocol:]filename.html#anchor
      		Load the named file, and move the cursor to the
      		first visible character after an <a name=anchor>
      		tag.  This is only useful for HTML files.

      	[protocol:]filename.ext?data
      		For the "file:" protocol, the data can be any valid
      		ex line address, including a "nomagic" regular
      		expression or a line number.  Elvis loads the file
      		and moves the cursor to the address.  This is an
      		Elvis-only extension!

      		For the "http:" protocol, the data is passed to the
      		HTTP server; it's interpretation is handled by the
      		HTTP server (or more likely a CGI script).

      		Either way, the data should be URL-encoded,
      		which means...
      			* + represents a space character
      			* %2B represents a '+' character
      			* %25 represents a '%' character
      			* %22 represents a '"' character
      			* %3C represents a '<' character
      			* %3E represents a '>' character
      			* Other printable ASCII characters can be
      			  given literally
      			* Anything else (non-ASCII characters or
      			  ASCII control characters) should be given
      			  as a '%' followed by two hex digits for
      			  its ordinal value.

<cite> ... </cite>
  These enclose a citation. Elvis displays the citation in italics.

  A citation is a reference to another document -- typically, this will be either the full name of the document, or symbol representing an entry in a bibliography; typically the symbol will be a pair of square brackets containing the first few letters of the author's name, and the last two digits of its year of publication. The bibliography should then provide the full title and other information about the cited document.

  For example, your document could contain "<cite>[JOY84]</cite>", and the corresponding bibliographic entry could look like this:

      	[JOY84] Joyce, Jim; "Interview with Bill Joy",
      		Unix Review magazine, August 1984.

<dfn> ... </dfn>
  These enclose a term that is being defined. Elvis displays the term in an emphasized font. Netscape doesn't support this tag, so you should probably avoid it. Use <em> ... </em> instead.
<em> ... </em>
  These enclose text which should be emphasized some way. Elvis displays the text in (you guessed it) italics.
<kbd> ... </kbd>
  These enclose text which the user might want to type into the computer some day. Generally, each word of the text will be the legend from a keytop on the user's keyboard, such as `Esc` or `Tab`. Elvis displays this text in boldface.
<strong> ... </strong>
  These enclose text which should be emphasized a heck of a lot. Elvis displays this text in boldface.
<var> ... </var>
  These enclose text which indicates where some variable argument is to be placed. Elvis displays this text in italics.
<address> ... </address>
  These enclose an address. Elvis displays the address in italics. Note that this is typically used for e-mail addresses and Web URLs, not postal addresses.
<code> ... </code>
  These enclose example code which is included in the body of a paragraph. Elvis displays the text in the fixed font -- which, unfortunately, looks exactly like the normal font on some printers.
<b> ... </b>
  The enclosed text is displayed in bold. The <strong> ... </strong> tags are preferred, if you really want to emphasize text.
<i> ... </i>
  The enclosed text is displayed in italics. The <em> ... </em> tags are preferred, if you really want to emphasize text.
<u> ... </u>
  The enclosed text is displayed underlined. You should avoid using this tag, because underlining is also used to indicate hypertext links. The <u> ... </u> text would look like a hypertext link but wouldn't work like one.
<tt> ... </tt>
  The enclosed text is displayed in the fixed font. The <code> ... </code> tags are preferred, if you really want to embed code examples in the body of a paragraph.

Note that most of these tags come in pairs, and the ending tag's name includes a '/' character. Elvis doesn't verify that the pairs match up correctly. Because of this, I strongly suggest that you preview your document using a more powerful HTML viewer such as Netscape before sharing it with the world. You may also want to run it through a checker such as weblint.

### 7.5.2 Character entities

Most text characters can be given literally in an HTML file, but some need special treatment. The most notable are <, >, &, and non-ASCII characters. HTML uses "character entities" to represent them.

Many of the entities are automatically derived from the digraph table. If you don't know about digraphs, you should look up the :digraph command, and the discussion on how to use them in input mode.

All of these must begin with an '&' character and end with a ';' character. In the earliest HTML standard, the ';' was optional, but Elvis requires it. If you omit the ';' from an entity, then Elvis will display it literally (not translate it to a single character).

Elvis supports the following character entities:

&lt; or &LT;
&gt; or &GT;
  The less-than and greater-than symbols (< and >).
&amp; or &AMP;
  The ampersand character character (&).
&quot; or &QUOT;
&ldquo;
&rdquo;
  The double-quote character (").
&lsquo;
&rsquo;
  The left and right single quote characters (‘ and ’).
&laquo;
&raquo;
  The left and right angle quote characters (« and »). These are formed from digraphs which combine two < characters or two > characters, respectively.
&nbsp; or &NBSP;
  A non-breaking space. This is displayed as a space character. It differs from plain old whitespace in that &nbsp; can't be converted into a line break.
&copy; or &COPY;
  The copyright symbol (©). Elvis looks for a digraph which combines a lowercase c and uppercase O. If there is no such digraph, then Elvis displays c.
&reg; or &REG;
  The registered trademark symbol (®). Elvis looks for a digraph which combines a lowercase r and uppercase O. If there is no such digraph, then Elvis displays r.
&pound;
&cent;
&yen;
&curren;
  Currency symbols (£, ¢, ¥, and ¤). These are formed from digraphs combining the letter L, C, Y or X (respectively) with the $ character.
&deg;
  The degree symbol (°). This is formed from a digraph combining two * characters.
&iexcl;
&iquest;
  Inverted exclamation mark and inverted question mark (¡ and ¿). These are formed from digraphs combining the ! or ? character (respectively) with the ~ character. If no such digraph exists, then the non-inverted version of that character is shown.
&shy;
  A small hyphen ().
&AElig;
  A digraph combining the letters A and E (Æ). If no such digraph has been defined, then Elvis will display E.
&aelig;
  A digraph combining the letters a and e (æ). If no such digraph has been defined, then Elvis will display e.
&ETH;
  A digraph combining a hyphen and the letter D (Ð).
&eth;
  A digraph combining a hyphen and the letter d (ð).
&THORN;
  A digraph combining the letters T and P (Þ), or just plain P if there is no such digraph.
&thorn;
  A digraph combining the letters t and p (þ), or just plain p if there is no such digraph.
&szlig;
  A digraph combining the letters s and z (ß), or just plain z if there is no such digraph.
&lettergrave;
  A digraph combining the ` and letter, such as &agrave; (à).
&letteracute;
  A digraph combining the ' and letter, such as &aacute; (á).
&lettercirc;
  A digraph combining the ^ and letter, such as &acirc; (â).
&lettertilde;
  A digraph combining the ~ and letter, such as &atilde; (ã).
&letteruml;
  A digraph combining the " and letter, such as &auml; (ä).
&letterring;
  A digraph combining the * and letter, such as &aring; (å).
&lettercedil;
  A digraph combining the , and letter, such as &ccedil; (ç).
&letterslash;
  A digraph combining the / and letter, such as &oslash; (ø).
&#number;
  The character whose ordinal value is number. This should be avoided, because you can't be sure which symbol set will be used when somebody else views the document. Some documents use &#160; which is a "hard" space in the ISO Latin-1 symbol set, but they should really use &nbsp;.

If your document uses a character entity which Elvis doesn't support, then Elvis will not convert that entity into a single character; instead, it will be displayed literally.

If Elvis looks for a digraph containing a punctuation character and a letter, and no such digraph has been defined, then Elvis will use the plain ASCII letter.

### 7.5.3 Using hypertext

The HTML hypertext has been implemented as a variation on the standard vi :tag command. Consequently, all of the wonderful commands that Elvis offers for browsing C source code can also be used for browsing HTML documents.

In EX mode, you can use :tag URL to pursue a hypertext reference, and :pop to come back afterward.

In VI mode, you can move the cursor onto the underlined text which denotes a hypertext reference, and hit ^] to pursue the reference, and ^T to come back afterward. Also, when in html mode the `Tab` key searches forward for the next hypertext reference, and the `Enter` key performs tag lookup just like the `^]` key.

If Elvis' user interface supports a mouse, then you can double-click the left button to follow a hypertext reference, and double-click the right button to come back afterward.

## 7.6 Man mode

The man display mode uses a markup language, as does the html display mode. The difference is that the man display mode's markup language resembles that of "troff -man". It is used for formatting entries in the UNIX user manuals.

Elvis supports only a tiny subset of the troff commands and -man macros. It is adequate for a surprising number of man pages, though. The most notable failing is the lack of number/string registers.

Commands which start with a "." are only recognized at the start of a line. The remainder of the line is used as arguments to the command. Commands which start with a "\" are recognized anywhere.

'\" letters
  On some Unix variants (but not Linux), if the first line of a man page begins with apostrophe-backslash-doublequote, then the rest of the line is interpreted as a list of letters indicating which preprocessors the page should be filtered through before being passed to troff. The most common letter is "`t`" for the tbl filter. Other letters may include "`e`" for eqn, "`p`" for pic, "`r`" for refer, and "`v`" for vgrind.

  Elvis doesn't use any of this because its table commands (`.TS` and `.TE`) are built in, and it doesn't support filtering while you edit anyway.

.\" comment
  Elvis ignores any text on a .\" command line.
.TH name section
  This command should appear at the top of the man page. It declares the name of the program to be described, and the section of the manual where it should appear. User programs are usually documented in section 1.
.SH name
  The name is displayed as a section header. If name contains whitespace, then it should be enclosed in quotes. Man pages usually have sections named NAME, SYNOPSIS, DESCRIPTION, OPTIONS, FILES, ENVIRONMENT, "SEE ALSO", BUGS, and AUTHOR, in that order. The "elvis.man" file is a typical example.
.SS name
  The name is displayed as a subsection header. If name contains whitespace, then it should be enclosed in quotes. Man pages rarely use subsections.
.B text
  The text is displayed in boldface.
.I text
  The text is displayed in italics.
.SM text
  Troff would display the text in a slightly smaller font. Elvis doesn't support multiple font sizes, though, so it simply outputs the text.
.RB text1 text2 ...
.BR text1 text2 ...
.RI text1 text2 ...
.IR text1 text2 ...
.BS text1 text2 ...
.SB text1 text2 ...
.ZN text1 text2 ...
  These output the argument text, alternating between two fonts. For example, .BR outputs the first argument word in boldface, the second in normal (a.k.a. Roman), the third in boldface again, and so on. The "S" font is supposed to be small, but Elvis uses the normal font for that. All whitespace is removed from between the argument words.

  The .ZN markup is nonstandard but common. It alternates between fixed and normal fonts.

.IP label indentation
  This starts an indented paragraph. The label is optional. If given, it is output before the paragraph, and without any extra indentation. This is typically used for presenting a term (the label) and its definition (the paragraph).

  The indentation is also optional. The indentation is given as a number followed by a letter indicating the unit size. Elvis accepts 'n' to indent by characters, 'i' to indent by inches, or 'p' to indent by points. For example, the command...

      	.IP \bu 3n

  ... would output a bullet and then indent the following text by two more characters. The default indent is 8n.
.TP
  This starts a hanging paragraph. That's like a .IP indented paragraph, except the label is declared on the line following the command, instead of on the command line itself. The body of the paragraph starts on the second line after the command line.

  Note that Elvis' version of `.TP` doesn't support an indentation parameter.

.P
.LP
.HP
  Any of these will start a regular paragraph. In addition, a series of one or more blank lines will also start a paragraph.
.RS
.RE
  These start and end a relative indentation, respectively. In other words, .RS increases the indentation of any subsequent text, and .RE reduces indentation.
.br
  This causes a line break.
.sp
  This causes a line break, and then leaves a blank line.
.nf
.fi
  These turn "fill mode" off and on, respectively. When fill mode is turned off, Elvis will perform much less formatting. It is similar to the <pre>...</pre> tags in HTML.
.TS
.TE
  In the real troff, these mark the start and end of a table, and the line after the .TS indicates the format of the table. For Elvis, these are just like .nf and .fi, respectively, except that .TS hides the line that follows it (so the table format is hidden). Elvis doesn't support multi-line formats, even though the real troff does. Here's an example:

      	.TS
      	r l.
      	1	one
      	10	ten
      	100	hundred
      	1000	thousand
      	.TE

  Try saving the above lines to a file named "table.man", and then running that file through tbl and nroff like this:

      	tbl table.man | nroff -man | more

.DS
.DE
  These mark the beginning and end of a "display." Inside the display, "fill mode" is turned off, just as it is for the .fi and .nf markups. The real troff tries to avoid page-breaks inside a display, but Elvis isn't that smart.
\e
  This is replaced by the backslash character.
\|
\&
\^
  These are deleted. If you ever feel a need to put a period at the start of a line, and don't want it to be treated like a command line, then put \&. in your file. The \& will prevent the period from being interpreted as the start of a command line, but will not show in the output.
\c
  This is deleted. Some man pages use these at the ends of lines.
\fB
\f1
  Switch to boldface.
\fI
\f2
  Switch to italics.
\fR
\f0
  Switch to the normal font.
\fP
  Switch to the default font for this context. That's boldface in headings, and normal the rest of the time. Actually, \fP is supposed to switch to the "previous" font, whatever that was, but Elvis doesn't do it that way.
\(XX
  This is used to access special characters, via a two-character name. Elvis supports just a few of these characters:

      .--------.----------------------------------------------.
      | Markup | What it looks like                           |
      |--------|----------------------------------------------|
      |  \(br  | |  Vertical line                             |
      |  \(bu  | *  Asterisk or bullet                        |
      |  \(co  | ©  Copyright symbol                          |
      |  \(dg  | ¡  Dagger (though Elvis shows inverted bang) |
      |  \(em  | -  Wide hyphen (Elvis shows normal hyphen)   |
      |  \(hy  | -  Narrow hyphen (Elvis shows normal hyphen) |
      |  \(lq  | "  Left quote                                |
      |  \(rn  | -  Horizontal line                           |
      |  \(rq  | "  Right quote                               |
      |  \(ul  | _  Underline character                       |
      ^--------^----------------------------------------------^

\*
\n
  In the real troff, these are used for accessing the value of a string or numeric register, respectively. Elvis doesn't support registers; it'll just display the \* or \n expression literally.

  There are a few exceptions, for strings that are normally predefined in the "man" macro package. Elvis does support the following strings:

      .--------.----------------------------------------------.
      | Markup | What it looks like                           |
      |--------|----------------------------------------------|
      |  \*R   | ®  Registered trademark symbol               |
      |  \*S   | (nothing - reverts to default font size)     |
      |  \*(Tm | TM General trademark symbol                  |
      |  \*(lq | "  Left quote                                |
      |  \*(rq | "  Right quote                               |
      ^--------^----------------------------------------------^

\character
  When character is something other than one of the above, output the character. In particular, \\ outputs a single backslash (though \e is the preferred notation).

Troff source was never designed to be interactively edited, and although I did the best I could, attempting to edit in "man" mode is still a disorienting experience. I suggest you get in the habit of using "normal" mode when making changes, and "man" mode to preview the effect of those changes. The ^Wd command makes switching between modes a pretty easy thing to do.

Unrecognized commands which start with "." are silently ignored.

Unrecognized commands which start with "\" will be output without the initial "\" character. This falls far short of the ideal, but there are just too many weird escapes to bother implementing in something that isn't being advertised as a troff clone. (NOTE: Elvis is not a troff clone.)

A tip: If your document contains sequences which look like \*X or \*(XY (for any characters X and Y), then it is trying to use defined strings. Look for a ".ds X foo" command near the top of the document to find out what that string is supposed to look like. The string \*(bu is a bullet character.

## 7.7 TeX mode

Don't get excited, this isn't that good. I spent two days adding a quick hack to the html/man display code to allow it to almost format some TeX documents. But the semantics of TeX are sufficiently different from HTML or `nroff -man` that a truly satisfying TeX formatter would need totally separate formatting code, which would require a couple of weeks to implement and would add about 25k bytes to the `elvis` executable. Since I don't use TeX myself, my priorities don't justify that. They justify a two-day hack and about 3k bytes of extra code.

### 7.7.1 Supported TeX markups

The following describes the subset of TeX that Elvis now supports. It also describes the quirks of Elvis' implementation.

%comment
  Anything between a `%` and the end of the line is ignored.
(blank lines)
\p
  Two or more consecutive newlines (i.e., one or more blank lines) indicate a paragraph break. You can also use `\p` to start a new paragraph; in fact, that's how all paragraph breaks are displayed if you set the list or showmarkups options.
{ ... }
  The `{` character causes the current font to be stored in a hidden memory location, and `}` resets the current font to the stored value. A few other markups, described below, use the { ... } notation for their arguments.

  This differs from TeX in two major ways:

  - In addition to the font, TeX stores other attributes such as the indentation level. Elvis only stores the font.
  - Elvis has only a single location for storing fonts, but TeX uses a stack, which allows you to nest { ... } pairs to good effect. Elvis will become confused by nested { ... } pairs.
\mathrelpunctuation
\charpunctuation
\punctuation
  These output the punctuation character literally. In the real TeX, `\mathrel` is more subtle than that.
\title{text}
  Display the text as a title: Centered, in the "bold" font.
\author{text}
  Display the text as an author name: Centered, in the "italic" font.
\section{text}
  Display the text as a section title: Starting at the leftmost column, in the "bold" font. Also, if it would be printed near the end of a page then it will be moved to the start of the next page instead.
\subsection{text}
  Display the text as a subsection title: Indented slightly from the left edge, and in the "bold" font.
\hline
  Draw a horizontal line across the page. Unfortunately, Elvis' implementation tends to leave a blank line above the horizontal line.
\begin{table}
\hfil or \hfill or &
\cr or \\
\end{table}
  These are used to present tables. `\cr` or `\\` marks the end of each row, and `\hfil, \hfill,` or `&` mark the end of a column's data within a row. TeX actually offers other commands to control the shape of the table, but Elvis doesn't support those commands.
\begin{quote}
\end{quote}
  These are used to enclose a quoted paragraph. Elvis uses extra indentation while displaying the paragraph.
\begin{verbatim}
\end{verbatim}
  These are used to enclose text which should be subjected to less processing; in particular, indentation and line breaks are preserved.
$$
  A `$$` pair toggles between the "normal" font with standard text filling, and the "fixed" font with lines displayed verbatim. This is typically used for presenting longer command-line examples on lines by themselves between paragraphs.
\begin{description}
\item[term]
\end{description}
  This is used for presenting a series of terms followed by their definitions.
\begin{enumerate}
\item
\end{enumerate}
  This is used for presenting a numbered list of items. Each item should be preceded by `\item`.
\begin{itemize}
\item
\item[bullet]
\end{itemize}
  This is used for presenting a list of items. Each item should be preceded either by `\item` to mark it with an asterisk, or by `\item[`bullet`]` to mark it with something other than an asterisk.
\tt
  Switch to the "fixed" font. Generally, all of these font-switching commands will be used with `{ ... }`, like this:

      Normal text {\tt Fixed-font text} Normal again.

\bf
  Switch to the "bold" font.
\em
\it
  Switch to the "italic" font.
\fo
  This is a common macro which indicates the following text is in a foreign language. Elvis supports it; it switches to the "italic" font.
$
  A single `$` character toggles between the "normal" font and the "fixed" font. This is often used for marking computer commands in the body of a paragraph.

### 7.7.2 Unsupported TeX markups

The following describes how Elvis deals with certain unsupported features of TeX.

\vspace{value}
  This is treated like a paragraph break.
\footnote{text}
  The footnote is completely hidden, including its text.
\halign...
\begin{tabular}...
\multicolumn...
\set...
\def...
\new...
\catcode...
\document...
\other=...
  Everything up to the end of the line is skipped. Other than that, the markup has no effect.
\other{text}
  The markup and its text are ignored.
\other
  Unrecognized markups are generally ignored. The single big exception is that if the markup is followed by punctuation or a backslash-space pair, then Elvis assumes the markup is probably just an abbreviation for some word or phrase which is supposed to be displayed in a special font; so Elvis displays the markup's name (without the leading backslash) in the "bold" font.