latex2e: Modes
17 Modes
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When LaTeX is processing your input text, it is always in one of three
modes:
* Paragraph mode
* Math mode
* Left-to-right mode, called LR mode for short
Mode changes occur only when entering or leaving an environment, or
when LaTeX is processing the argument of certain text-producing
commands.
"Paragraph mode" is the most common; it's the one LaTeX is in when
processing ordinary text. In this mode, LaTeX breaks the input text
into lines and breaks the lines into pages.
LaTeX is in "math mode" when it's generating a mathematical formula,
either displayed math or within a line.
In "LR mode", as in paragraph mode, LaTeX considers the output that
it produces to be a string of words with spaces between them. 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
'\mbox', LaTeX would keep typesetting them from left to right inside a
single box (and then most likely complain because the resulting box was
too wide to fit on the line). LaTeX is in LR mode when it starts making
a box with an '\mbox' 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.
There are also several text-producing commands and environments for
making a box that put LaTeX into paragraph mode. The box made by one of
these commands or environments will be called a 'parbox'. When LaTeX is
in paragraph mode while making a box, it is said to be in "inner
paragraph mode" (no page breaks). Its normal paragraph mode, which it
starts out in, is called "outer paragraph mode".
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