% underscore.sty     21-Sep-2005   Donald Arseneau   asnd@triumf.ca

% Make the "_" character print as "\textunderscore" in text.

% Copyright 1998,2001,2005,2006 Donald Arseneau;  

% License: LPPL version 1.2 or later.

% Instructions follow after the definitions.

\ProvidesPackage{underscore}[2006/09/13]

\begingroup

 \catcode`\_=\active

 \gdef _{% \relax % No relax gives a small vulnerability in alignments

   \ifx\if@safe@actives\iftrue % must be outermost test!

      \string_%

   \else

      \ifx\protect\@typeset@protect

         \ifmmode \sb \else \BreakableUnderscore \fi

      \else

         \ifx\protect\@unexpandable@protect \noexpand_%

         \else \protect_%

      \fi\fi

    \fi}

  \global\let\ActiveUnderscore=_

  \gdef\normalUnderscoreDef{\let_\ActiveUnderscore}

\endgroup

% At begin: set catcode; fix \long \ttdefault so I can use it in comparisons; 

% reapply definition of active _ in output routine (\@firstofone to strip

% away braces, so avoiding deeper nesting).

\AtBeginDocument{%

  {\immediate\write\@auxout{\catcode\number\string`\_ \string\active}}%

  \catcode\string`\_\string=\active

  \edef\ttdefault{\ttdefault}%

  \output=\expandafter\expandafter\expandafter

     {\expandafter\expandafter\expandafter\normalUnderscoreDef

      \expandafter\@firstofone\the\output}%

}

\newcommand{\BreakableUnderscore}{\leavevmode\nobreak\hskip\z@skip

 \ifx\f@family\ttdefault \string_\else \textunderscore\fi

 \usc@dischyph\nobreak\hskip\z@skip}

\DeclareRobustCommand{\_}{%

  \ifmmode \nfss@text{\textunderscore}\else \BreakableUnderscore \fi}

\let\usc@dischyph\@dischyph

\DeclareOption{nohyphen}{\def\usc@dischyph{\discretionary{}{}{}}}

\DeclareOption{strings}{\catcode`\_=\active}

\ProcessOptions

\ifnum\catcode`\_=\active\else \endinput \fi

%%%%%%%%   Redefine commands that use character strings   %%%%%%%%

\@ifundefined{UnderscoreCommands}{\let\UnderscoreCommands\@empty}{}

\expandafter\def\expandafter\UnderscoreCommands\expandafter{%

  \UnderscoreCommands

  \do\include \do\includeonly

  \do\@input \do\@iinput \do\InputIfFileExists

  \do\ref \do\pageref \do\newlabel

  \do\bibitem \do\@bibitem \do\cite \do\nocite \do\bibcite

  \do\Ginclude@graphics \do\@setckpt

}

% Macro to redefine a macro to pre-process its string argument

% with \protect -> \string.

\def\do#1{% Avoid double processing if user includes command twice!

 \@ifundefined{US\string_\expandafter\@gobble\string#1}{%

   \edef\@tempb{\meaning#1}% Check if macro is just a protection shell...

   \def\@tempc{\protect}%

   \edef\@tempc{\meaning\@tempc\string#1\space\space}%

   \ifx\@tempb\@tempc % just a shell: hook into the protected inner command

     \expandafter\do

       \csname \expandafter\@gobble\string#1 \expandafter\endcsname

   \else % Check if macro takes an optional argument

     \def\@tempc{\@ifnextchar[}%

     \edef\@tempa{\def\noexpand\@tempa####1\meaning\@tempc}%

     \@tempa##2##3\@tempa{##2\relax}%

     \edef\@tempb{\meaning#1\meaning\@tempc}%

     \edef\@tempc{\noexpand\@tempd \csname

        US\string_\expandafter\@gobble\string#1\endcsname}%

     \if \expandafter\@tempa\@tempb \relax 12\@tempa % then no optional arg

       \@tempc #1\US@prot

     \else  % There is optional arg

       \@tempc #1\US@protopt

     \fi

   \fi

 }{}}

\def\@tempd#1#2#3{\let#1#2\def#2{#3#1}}

\def\US@prot#1#2{\let\@@protect\protect \let\protect\string

  \edef\US@temp##1{##1{#2}}\restore@protect\US@temp#1}

\def\US@protopt#1{\@ifnextchar[{\US@protarg#1}{\US@prot#1}}

\def\US@protarg #1[#2]{\US@prot{{#1[#2]}}}

\UnderscoreCommands

\let\do\relax \let\@tempd\relax  % un-do

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\endinput

underscore.sty    13-Sep-2006  Donald Arseneau

Features:

~~~~~~~~~

The "\_" command (which normally prints an underscore character or

facsimile) is altered so that the hyphenation of constituent words

is not affected, and hyphenation is permitted after the underscore.

For example, "compound\_fracture" hyphenates as com- pound\_- frac- ture.

If you prefer the underscore to break without a hyphen (but still with 

the same rules for explicit hyphen-breaks) then use the [nohyphen]

package option.

A simple "_" acts just like "\_" in text mode, but makes a subscript

in math mode: activation_energy $E_a$

Both forms use an underscore character if the font encoding contains

one (e.g., "\usepackage[T1]{fontenc}" or typewriter fonts in any encoding),

but they use a rule if there is no proper character.

Deficiencies:

~~~~~~~~~~~~~

The skips and penalties ruin any kerning with the underscore character

(when a character is used).  However, there doesn't seem to be much, if

any, such kerning in the ec fonts, and there is never any kerning with

a rule.

You must avoid "_" in file names and in cite or ref tags, or you must use 

the babel package, with its active-character controls, or you must give 

the [strings] option, which attempts to redefine several commands (and 

may not work perfectly).  Even without the [strings] option or babel, you 

can use occasional underscores like: "\include{file\string_name}".

Option: [strings]

~~~~~~~~~~~~~~~~~

The default operation is quite simple and needs no customization; but

you must avoid using "_" in any place where LaTeX uses an argument as

a string of characters for some control function or as a name.  These

include the tags for "\cite" and "\ref", file names for "\input", 

"\include", and "\includegraphics", environment names, counter names,

and placement parameters (like "[t]").  The problem with these contexts

is that they are `moving arguments' but LaTeX does not `switch on' the

"\protect" mechanism for them.

If you need to use the underscore character in these places, the package

option [strings] is provided to redefine commands that take such a string

argument so that protection is applied (with "\protect" being "\string").

The list of commands is given in "\UnderscoreCommands", with "\do" before

each; plus several others covering "\input", "\includegraphics, "\cite", 

"\ref", and their variants.  Not included are many commands regarding font 

names, everything with counter names, environment names, page styles, and 

versions of "\ref" and "\cite" defined by external packages (e.g., "\vref" 

and "\citeyear").

You can add to the list of supported commands by defining "\UnderscoreCommands"

before loading this package; e.g.

   \usepackage{chicago}

   \newcommand{\UnderscoreCommands}{%   (\cite already done)

     \do\citeNP \do\citeA \do\citeANP \do\citeN \do\shortcite

     \do\shortciteNP \do\shortciteA \do\shortciteANP \do\shortciteN

     \do\citeyear \do\citeyearNP

   }

   \usepackage[strings]{underscore}

Not all commands can be supported this way!  Only commands that take a

string argument *first* can be protected.  One optional argument before

the string argument is also permitted, as exemplified by "\cite": both

"\cite{tags}" and "\cite[text]{tags}" are allowed.  A command like

"\@addtoreset" which takes two counter names as arguments could not

be protected by listing it in "\UnderscoreCommands".

*When you use the [strings] option, you must load this package

last* (or nearly last).

There are two reasons: 1) The redefinitions done for protection must come

after other packages define their customized versions of those commands.

2) The [strings] option requires the "_" character to be activated immediately

in order for the cite and ref tags to be read properly from the .aux file

as plain strings, and this catcode setting might disrupt other packages.

The babel package implements a protection mechanism for many commands,

and will be a complete fix for most documents without the [strings] option.

Many add-on packages are compatible with babel, so they will get the

strings protection also.  However, there are several commands that are 

not covered by babel, but can easily be supported by the [strings] and 

"\UnderscoreCommands" mechanism.  Beware that using both [strings] and

babel might lead to conflicts, but none are seen yet (load babel last).

Implementation Notes:

~~~~~~~~~~~~~~~~~~~~~

The first setting of "_" to be an active character is performed in a local

group so as to not interfere with other packages.  The catcode setting

is repeated with "\AtBeginDocument" so the definition is in effect for the

text.  However, the catcode setting is repeated immediately when the

[strings] option is detected.

The definition of the active "_" is essentially:

       \ifmmode \sb \else \BreakableUnderscore \fi

where "\sb" retains the normal subscript meaning of "_" and where

"\BreakableUnderscore" is essentially "\_".  The rest of the definition

handles the "\protect"ion without causing "\relax" to be inserted before

the character.

"\BreakableUnderscore" uses "\nobreak\hskip\z@skip" to separate the

underscore from surrounding words, thus allowing TeX to hyphenate them,

but preventing free breaks around the underscore. Next, it checks the

current font family, and uses the underscore character from tt fonts or

otherwise "\textunderscore" (which is a character or rule depending on

the font encoding).  After the underscore, it inserts a discretionary

hyphenation point as "\usc@dischyph", which is usually just "\-"

except that it still works in the tabbing environment, although it

will give "\discretionary{}{}{}" under the [nohyphen] option.  After

that, another piece of non-breaking interword glue is inserted. 

Ordinarily, the comparison "\ifx\f@family\ttdefault" will always fail 

because "\ttdefault" is `long' whereas "\f@family" is not (boooo hisss),

but "\ttdefault" is redefined to be non-long by "\AtBeginDocument".

The "\_" command is then defined to use "\BreakableUnderscore".

If the [strings] option is not given, then that is all!

Under the [strings] option, the list of special commands is processed to:

 - retain the original command as "\US_"*command* (e.g., "\US_ref")

 - redefine the command as "\US@prot\US_command" for ordinary commands

   ("\US@prot\US_ref") or as "\US@protopt\US_command" when an optional

   argument is possible (e.g., "\US@protopt\US_bibitem").

 - self-protecting commands ("\cite") retain their self-protection.

Diagnosing the state of the pre-existing command is done by painful

contortions involving "\meaning".

"\US@prot" and "\US@protopt" read the argument, process it with 

"\protect" enabled, then invoke the saved "\US_command".

Modifications:

~~~~~~~~~~~~~~

13-Sep-2006  Reassert my definition in the output routine (listings).

21-Sep-2005  \includegraphics safe.

12-Oct-2001  Babel (safe@actives) compatibility and [nohyphen] option.

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