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<html>
<head><title>Help On LaTeX Modes</title></head>
<body bgcolor="#ffffff" text="#000000" link="#000099" vlink="#cc0000" alink="#cc0000">
<h1><font size="-2">Hypertext Help with LaTeX</font><br><font color="#cc0000">Modes</font></h1>
<p>
 When LaTeX is processing your input text, it is always in one of three
 modes:
<ul>
  <li><I>Paragraph</I> mode
  <li><I>Math</I> mode
  <li><I>Left-to-right</I> mode, called LR mode for short
</ul>

 LaTeX  changes  mode only when  it goes  up or down  a staircase  to a
 different  level, though not all level changes  produce  mode changes.
 Mode changes occur only when entering  or leaving  an environment,  or
 when  LaTeX  is processing  the  argument  of  certain  text-producing
 commands. 
<h2>Paragraph mode</h2>
 Paragraph  mode  is the most  common;  it's  the one LaTeX  is in when
 processing  ordinary  text.  In that mode, LaTeX breaks your text into
 lines and breaks  the lines  into pages. 
<p>
 There
 are also several text-producing commands and environments for making a
 box that put LaTeX  in paragraph  mode.   The box made by one of these
 commands  or environments  will be called a 
 <a href="ltx-294.html">parbox</a>.   When LaTeX is in
 paragraph mode while making a box, it is said to be in inner paragraph
 mode.  The normal  paragraph  mode, in which LaTeX starts  out, is called
 outer paragraph mode. 

<h2>Math mode</h2> 
 LaTeX  is in math mode when it's generating a mathematical formula. It is
 in math mode in the <a href="ltx-115.html#math">math</a>, 
 <a href="ltx-421.html">displaymath</a>, <a href="ltx-224.html">equation</a>,
 and <a href="ltx-223.html"> eqnarray</a> environments.
<p>
 In math mode letters are assumed to be math symbols and spaced accordingly.
 Spaces in the input are ignored, except that spaces may be needed to 
 delineate the end of commands.

<h2>LR mode</h2>
 In LR mode, as in paragraph
 mode, LaTeX considers  the output that it produces  to be a string  of
 words with spaces between them. In LR mode, unlike paragraph and math modes,
 spaces are not ignored; an input space creates an output space. 
 However, unlike paragraph mode, LaTeX
 keeps going from left to right; it never starts a new line in LR mode. 
 Even  if you put a hundred  words  into  an 
 <a href="ltx-265.html"><tt>\mbox</tt></a>,  LaTeX  would  keep
 typesetting  them from left to right  inside  a single  box,  and then
 complain because the resulting box was too wide to fit on the line.
<p>
 LaTeX is in LR mode when it starts making a box with an 
 <a href="ltx-265.html"><tt>\mbox</tt></a> command. 
 You can get it to enter a different mode inside the box - for example,
 you can make it enter  math mode to put a formula  in the box.  
<hr>
Also see <a href="ltx-115.html">Math Formulas</a><br>
Go to <a href="ltx-2.html">LaTeX Table of Contents</a><br>
<hr>
<address>
Revised: Sheldon Green, 31 May 1995.
</address>
</body>
</html>