+<div class="doc_text">
+
+<p>Positional arguments are those arguments that are not named, and are not
+specified with a hyphen. Positional arguments should be used when an option is
+specified by its position alone. For example, the standard Unix <tt>grep</tt>
+tool takes a regular expression argument, and an optional filename to search
+through (which defaults to standard input if a filename is not specified).
+Using the CommandLine library, this would be specified as:</p>
+
+<pre>
+<a href="#cl::opt">cl::opt</a><string> Regex (<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><regular expression></i>"), <a href="#cl::Required">cl::Required</a>);
+<a href="#cl::opt">cl::opt</a><string> Filename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <a href="#cl::init">cl::init</a>("<i>-</i>"));
+</pre>
+
+<p>Given these two option declarations, the <tt>--help</tt> output for our grep
+replacement would look like this:</p>
+
+<pre>
+USAGE: spiffygrep [options] <b><regular expression> <input file></b>
+
+OPTIONS:
+ -help - display available options (--help-hidden for more)
+</pre>
+
+<p>... and the resultant program could be used just like the standard
+<tt>grep</tt> tool.</p>
+
+<p>Positional arguments are sorted by their order of construction. This means
+that command line options will be ordered according to how they are listed in a
+.cpp file, but will not have an ordering defined if they positional arguments
+are defined in multiple .cpp files. The fix for this problem is simply to
+define all of your positional arguments in one .cpp file.</p>
+
+</div>
+
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="--">Specifying positional options with hyphens</a>
+</div>
+
+<div class="doc_text">
+
+<p>Sometimes you may want to specify a value to your positional argument that
+starts with a hyphen (for example, searching for '<tt>-foo</tt>' in a file). At
+first, you will have trouble doing this, because it will try to find an argument
+named '<tt>-foo</tt>', and will fail (and single quotes will not save you).
+Note that the system <tt>grep</tt> has the same problem:</p>
+
+<pre>
+ $ spiffygrep '-foo' test.txt
+ Unknown command line argument '-foo'. Try: spiffygrep --help'
+
+ $ grep '-foo' test.txt
+ grep: illegal option -- f
+ grep: illegal option -- o
+ grep: illegal option -- o
+ Usage: grep -hblcnsviw pattern file . . .
+</pre>
+
+<p>The solution for this problem is the same for both your tool and the system
+version: use the '<tt>--</tt>' marker. When the user specifies '<tt>--</tt>' on
+the command line, it is telling the program that all options after the
+'<tt>--</tt>' should be treated as positional arguments, not options. Thus, we
+can use it like this:</p>
+
+<pre>
+ $ spiffygrep -- -foo test.txt
+ ...output...
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a>
+</div>
+
+<div class="doc_text">
+
+<p>The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> is
+used to construct programs that use "interpreter style" option processing. With
+this style of option processing, all arguments specified after the last
+positional argument are treated as special interpreter arguments that are not
+interpreted by the command line argument.</p>
+
+<p>As a concrete example, lets say we are developing a replacement for the
+standard Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first
+you specify options to the shell itself (like <tt>-x</tt> which turns on trace
+output), then you specify the name of the script to run, then you specify
+arguments to the script. These arguments to the script are parsed by the bourne
+shell command line option processor, but are not interpreted as options to the
+shell itself. Using the CommandLine library, we would specify this as:</p>
+
+<pre>
+<a href="#cl::opt">cl::opt</a><string> Script(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input script></i>"), <a href="#cl::init">cl::init</a>("-"));
+<a href="#cl::list">cl::list</a><string> Argv(<a href="#cl::ConsumeAfter">cl::ConsumeAfter</a>, <a href="#cl::desc">cl::desc</a>("<i><program arguments>...</i>"));
+<a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>"));
+</pre>
+
+<p>which automatically provides the help output:</p>
+
+<pre>
+USAGE: spiffysh [options] <b><input script> <program arguments>...</b>
+
+OPTIONS:
+ -help - display available options (--help-hidden for more)
+ <b>-x - Enable trace output</b>
+</pre>
+
+<p>At runtime, if we run our new shell replacement as '<tt>spiffysh -x test.sh
+-a -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the
+<tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the
+<tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because they
+were specified after the last positional argument (which is the script
+name).</p>
+
+<p>There are several limitations to when <tt>cl::ConsumeAfter</tt> options can
+be specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified
+per program, there must be at least one <a href="#positional">positional
+argument</a> specified, and the <tt>cl::ConsumeAfter</tt> option should be a <a
+href="#cl::list">cl::list</a> option.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="subsection">
+ <a name="storage">Internal vs External Storage</a>
+</div>
+
+<div class="doc_text">
+
+<p>By default, all command line options automatically hold the value that they
+parse from the command line. This is very convenient in the common case,
+especially when combined with the ability to define command line options in the
+files that use them. This is called the internal storage model.</p>
+
+<p>Sometimes, however, it is nice to separate the command line option processing
+code from the storage of the value parsed. For example, lets say that we have a
+'<tt>-debug</tt>' option that we would like to use to enable debug information
+across the entire body of our program. In this case, the boolean value
+controlling the debug code should be globally accessable (in a header file, for
+example) yet the command line option processing code should not be exposed to
+all of these clients (requiring lots of .cpp files to #include
+<tt>CommandLine.h</tt>).</p>
+
+<p>To do this, set up your .h file with your option, like this for example:</p>
+
+<pre>
+<i>// DebugFlag.h - Get access to the '-debug' command line option
+//
+
+// DebugFlag - This boolean is set to true if the '-debug' command line option
+// is specified. This should probably not be referenced directly, instead, use
+// the DEBUG macro below.
+//</i>
+extern bool DebugFlag;
+
+<i>// DEBUG macro - This macro should be used by code to emit debug information.
+// In the '-debug' option is specified on the command line, and if this is a
+// debug build, then the code specified as the option to the macro will be
+// executed. Otherwise it will not be. Example:
+//
+// DEBUG(cerr << "Bitset contains: " << Bitset << "\n");
+//</i>
+<span class="doc_red">#ifdef NDEBUG
+#define DEBUG(X)
+#else
+#define DEBUG(X)</span> \
+ do { if (DebugFlag) { X; } } while (0)
+<span class="doc_red">#endif</span>
+</pre>
+
+<p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the
+<tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to
+set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass
+an additial argument to our command line argument processor, and we specify
+where to fill in with the <a href="#cl::location">cl::location</a>
+attribute:</p>
+
+<pre>
+bool DebugFlag; <i>// the actual value</i>
+static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i>
+Debug("<i>debug</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable debug output</i>")</a>, <a href="#cl::Hidden">cl::Hidden</a>,
+ <a href="#cl::location">cl::location</a>(DebugFlag));
+</pre>
+
+<p>In the above example, we specify "<tt>true</tt>" as the second argument to
+the <a href="#cl::opt">cl::opt</a> template, indicating that the template should
+not maintain a copy of the value itself. In addition to this, we specify the <a
+href="#cl::location">cl::location</a> attribute, so that <tt>DebugFlag</tt> is
+automatically set.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="attributes">Option Attributes</a>
+</div>
+
+<div class="doc_text">
+
+<p>This section describes the basic attributes that you can specify on
+options.</p>
+
+<ul>
+
+<li>The option name attribute (which is required for all options, except <a
+href="#positional">positional options</a>) specifies what the option name is.
+This option is specified in simple double quotes:
+
+<pre>
+<a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>");
+</pre>
+
+</li>
+
+<li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a
+description for the option to be shown in the <tt>--help</tt> output for the
+program.</li>
+
+<li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute
+specifies a string that can be used to fine tune the <tt>--help</tt> output for
+a command line option. Look <a href="#value_desc_example">here</a> for an
+example.</li>
+
+<li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an
+inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is
+not specified then the command line option value defaults to the value created
+by the default constructor for the type. <b>Warning</b>: If you specify both
+<b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option,
+you must specify <b><tt>cl::location</tt></b> first, so that when the
+command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the
+initial value. (You will get an error at runtime if you don't put them in
+the right order.)</li>
+
+<li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where to
+store the value for a parsed command line option if using external storage. See
+the section on <a href="#storage">Internal vs External Storage</a> for more
+information.</li>
+
+<li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute
+specifies which option a <a href="#cl::alias">cl::alias</a> option is an alias
+for.</li>
+
+<li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies
+the string-to-value mapping to be used by the generic parser. It takes a
+<b>null terminated</b> list of (option, value, description) triplets that
+specify the option name, the value mapped to, and the description shown in the
+<tt>--help</tt> for the tool. Because the generic parser is used most
+frequently with enum values, two macros are often useful:
+
+<ol>
+
+<li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a
+nice simple way to specify a triplet for an enum. This macro automatically
+makes the option name be the same as the enum name. The first option to the
+macro is the enum, the second is the description for the command line
+option.</li>
+
+<li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to
+specify macro options where the option name doesn't equal the enum name. For
+this macro, the first argument is the enum value, the second is the flag name,
+and the second is the description.</li>
+
+</ol>
+
+You will get a compile time error if you try to use cl::values with a parser
+that does not support it.</li>
+
+</ul>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="modifiers">Option Modifiers</a>
+</div>
+
+<div class="doc_text">
+
+<p>Option modifiers are the flags and expressions that you pass into the
+constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
+href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to
+tweak how options are parsed and how <tt>--help</tt> output is generated to fit
+your application well.</p>
+
+<p>These options fall into five main catagories:</p>
+
+<ol>
+<li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a></li>
+<li><a href="#numoccurrences">Controlling the number of occurrences
+ required and allowed</a></li>
+<li><a href="#valrequired">Controlling whether or not a value must be
+ specified</a></li>
+<li><a href="#formatting">Controlling other formatting options</a></li>
+<li><a href="#misc">Miscellaneous option modifiers</a></li>
+</ol>
+
+<p>It is not possible to specify two options from the same catagory (you'll get
+a runtime error) to a single option, except for options in the miscellaneous
+catagory. The CommandLine library specifies defaults for all of these settings
+that are the most useful in practice and the most common, which mean that you
+usually shouldn't have to worry about these.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="hiding">Hiding an option from <tt>--help</tt> output</a>
+</div>
+
+<div class="doc_text">
+
+<p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and
+<tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option
+appears in the <tt>--help</tt> and <tt>--help-hidden</tt> output for the
+compiled program:</p>
+
+<ul>
+
+<li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier
+(which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
+href="#cl::list">cl::list</a></tt> options), indicates the option is to appear
+in both help listings.</li>
+
+<li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the
+default for <tt><a href="#cl::alias">cl::alias</a></tt> options), indicates that
+the option should not appear in the <tt>--help</tt> output, but should appear in
+the <tt>--help-hidden</tt> output.</li>
+
+<li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier,
+indicates that the option should not appear in any help output.</li>
+
+</ul>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="numoccurrences">Controlling the number of occurrences required and
+ allowed</a>
+</div>
+
+<div class="doc_text">
+
+<p>This group of options is used to control how many time an option is allowed
+(or required) to be specified on the command line of your program. Specifying a
+value for this setting allows the CommandLine library to do error checking for
+you.</p>
+
+<p>The allowed values for this option group are:</p>
+
+<ul>
+
+<li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which
+is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
+href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will
+allow either zero or one occurrence of the option to be specified.</li>
+
+<li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier
+(which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class)
+indicates that your program will allow the option to be specified zero or more
+times.</li>
+
+<li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier
+indicates that the specified option must be specified exactly one time.</li>
+
+<li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier
+indicates that the option must be specified at least one time.</li>
+
+<li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a
+href="#positional">Positional arguments section</a></li>
+
+</ul>
+
+<p>If an option is not specified, then the value of the option is equal to the
+value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If
+the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the
+option value is initialized with the default constructor for the data type.</p>
+
+<p>If an option is specified multiple times for an option of the <tt><a
+href="#cl::opt">cl::opt</a></tt> class, only the last value will be
+retained.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="valrequired">Controlling whether or not a value must be specified</a>
+</div>
+
+<div class="doc_text">
+
+<p>This group of options is used to control whether or not the option allows a
+value to be present. In the case of the CommandLine library, a value is either
+specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing
+string (e.g. '<tt>-o a.out</tt>').</p>
+
+<p>The allowed values for this option group are:</p>
+
+<ul>
+
+<li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier
+(which is the default for <tt>bool</tt> typed options) specifies that it is
+acceptable to have a value, or not. A boolean argument can be enabled just by
+appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'.
+If an option is specified with this mode, it is illegal for the value to be
+provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To
+get this behavior, you must use the <a
+href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li>
+
+<li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier
+(which is the default for all other types except for <a
+href="#onealternative">unnamed alternatives using the generic parser</a>)
+specifies that a value must be provided. This mode informs the command line
+library that if an option is not provides with an equal sign, that the next
+argument provided must be the value. This allows things like '<tt>-o
+a.out</tt>' to work.</li>
+
+<li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a>
+modifier (which is the default for <a href="#onealternative">unnamed
+alternatives using the generic parser</a>) indicates that it is a runtime error
+for the user to specify a value. This can be provided to disallow users from
+providing options to boolean options (like '<tt>-foo=true</tt>').</li>
+
+</ul>
+
+<p>In general, the default values for this option group work just like you would
+want them to. As mentioned above, you can specify the <a
+href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean
+argument to restrict your command line parser. These options are mostly useful
+when <a href="#extensionguide">extending the library</a>.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="formatting">Controlling other formatting options</a>
+</div>
+
+<div class="doc_text">
+
+<p>The formatting option group is used to specify that the command line option
+has special abilities and is otherwise different from other command line
+arguments. As usual, you can only specify at most one of these arguments.</p>
+
+<ul>
+
+<li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a>
+modifier (which is the default all options) specifies that this option is
+"normal".</li>
+
+<li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier
+specifies that this is a positional argument, that does not have a command line
+option associated with it. See the <a href="#positional">Positional
+Arguments</a> section for more information.</li>
+
+<li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier
+specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li>
+
+<li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies
+that this option prefixes its value. With 'Prefix' options, there is no equal
+sign that separates the value from the option name specified. This is useful
+for processing odd arguments like '<tt>-lmalloc -L/usr/lib'</tt> in a linker
+tool. Here, the '<tt>l</tt>' and '<tt>L</tt>' options are normal string (list)
+options, that have the <a href="#cl::Prefix">cl::Prefix</a> modifier added to
+allow the CommandLine library to recognize them. Note that <a
+href="#cl::Prefix">cl::Prefix</a> options must not have the <a
+href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier specified.</li>
+
+<li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used
+to implement unix style tools (like <tt>ls</tt>) that have lots of single letter
+arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>'
+command actually enables four different options, all of which are single
+letters. Note that <a href="#cl::Grouping">cl::Grouping</a> options cannot have
+values.</li>
+
+</ul>
+
+<p>The CommandLine library does not restrict how you use the <a
+href="#cl::Prefix">cl::Prefix</a> or <a href="#cl::Grouping">cl::Grouping</a>
+modifiers, but it is possible to specify ambiguous argument settings. Thus, it
+is possible to have multiple letter options that are prefix or grouping options,
+and they will still work as designed.</p>
+
+<p>To do this, the CommandLine library uses a greedy algorithm to parse the
+input option into (potentially multiple) prefix and grouping options. The
+strategy basically looks like this:</p>
+
+<p><tt>parse(string OrigInput) {</tt>
+<ol>
+<li><tt>string input = OrigInput;</tt>
+<li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i>
+<li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i>
+<li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i>
+<li><tt>if (getOption(input).isPrefix())<br>
+ return getOption(input).parse(input);</tt>
+<li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br>
+ getOption(input).parse();<br>
+ OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br>
+ input = OrigInput;<br>
+ while (!isOption(input) && !input.empty()) input.pop_back();<br>
+}</tt>
+<li><tt>if (!OrigInput.empty()) error();</tt>
+</tt>
+
+</ol>
+<tt>}</tt></p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="misc">Miscellaneous option modifiers</a>
+</div>
+
+<div class="doc_text">
+
+<p>The miscellaneous option modifiers are the only flags where you can specify
+more than one flag from the set: they are not mutually exclusive. These flags
+specify boolean properties that modify the option.</p>
+
+<ul>
+
+<li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier
+indicates that any commas specified for an option's value should be used to
+split the value up into multiple values for the option. For example, these two
+options are equivalent when <tt>cl::CommaSeparated</tt> is specified:
+"<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only
+makes sense to be used in a case where the option is allowed to accept one or
+more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li>
+
+</ul>
+
+<p>So far, the only miscellaneous option modifier is the
+<tt>cl::CommaSeparated</tt> modifier.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="toplevel">Top-Level Classes and Functions</a>
+</div>
+
+<div class="doc_text">
+
+<p>Despite all of the built-in flexibility, the CommandLine option library
+really only consists of one function (<a
+href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>)
+and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a
+href="#cl::list"><tt>cl::list</tt></a>, and <a
+href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three
+classes in detail.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt>
+ function</a>
+</div>
+
+<div class="doc_text">
+
+<p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called
+directly from <tt>main</tt>, and is used to fill in the values of all of the
+command line option variables once <tt>argc</tt> and <tt>argv</tt> are
+available.</p>
+
+<p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters
+(<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter
+which holds <a href="#description">additional extra text</a> to emit when the
+<tt>--help</tt> option is invoked.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt>
+ function</a>
+</div>
+
+<div class="doc_text">
+
+<p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects
+as <a
+href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>,
+except that it is designed to take values for options from an environment
+variable, for those cases in which reading the command line is not convenient or
+not desired. It fills in the values of all the command line option variables
+just like <a
+href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
+does.</p>
+
+<p>It takes three parameters: first, the name of the program (since
+<tt>argv</tt> may not be available, it can't just look in <tt>argv[0]</tt>),
+second, the name of the environment variable to examine, and third, the optional
+<a href="#description">additional extra text</a> to emit when the
+<tt>--help</tt> option is invoked.</p>
+
+<p><tt>cl::ParseEnvironmentOptions</tt> will break the environment
+variable's value up into words and then process them using
+<a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>.
+<b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support
+quoting, so an environment variable containing <tt>-option "foo bar"</tt> will
+be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>,
+which is different from what you would get from the shell with the same
+input.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="cl::opt">The <tt>cl::opt</tt> class</a>
+</div>
+
+<div class="doc_text">
+
+<p>The <tt>cl::opt</tt> class is the class used to represent scalar command line
+options, and is the one used most of the time. It is a templated class which
+can take up to three arguments (all except for the first have default values
+though):</p>
+
+<pre>
+<b>namespace</b> cl {
+ <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>,
+ <b>class</b> ParserClass = parser<DataType> >
+ <b>class</b> opt;
+}
+</pre>
+
+<p>The first template argument specifies what underlying data type the command
+line argument is, and is used to select a default parser implementation. The
+second template argument is used to specify whether the option should contain
+the storage for the option (the default) or whether external storage should be
+used to contain the value parsed for the option (see <a href="#storage">Internal
+vs External Storage</a> for more information).</p>
+
+<p>The third template argument specifies which parser to use. The default value
+selects an instantiation of the <tt>parser</tt> class based on the underlying
+data type of the option. In general, this default works well for most
+applications, so this option is only used when using a <a
+href="#customparser">custom parser</a>.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="cl::list">The <tt>cl::list</tt> class</a>
+</div>
+
+<div class="doc_text">
+
+<p>The <tt>cl::list</tt> class is the class used to represent a list of command
+line options. It too is a templated class which can take up to three
+arguments:</p>
+
+<pre>
+<b>namespace</b> cl {
+ <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
+ <b>class</b> ParserClass = parser<DataType> >
+ <b>class</b> list;
+}
+</pre>
+
+<p>This class works the exact same as the <a
+href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is
+the <b>type</b> of the external storage, not a boolean value. For this class,
+the marker type '<tt>bool</tt>' is used to indicate that internal storage should
+be used.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="cl::alias">The <tt>cl::alias</tt> class</a>
+</div>
+
+<div class="doc_text">
+
+<p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form
+aliases for other arguments.</p>
+
+<pre>
+<b>namespace</b> cl {
+ <b>class</b> alias;
+}
+</pre>
+
+<p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be
+used to specify which option this is an alias for. Alias arguments default to
+being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do
+the conversion from string to data.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="builtinparsers">Builtin parsers</a>
+</div>
+
+<div class="doc_text">
+
+<p>Parsers control how the string value taken from the command line is
+translated into a typed value, suitable for use in a C++ program. By default,
+the CommandLine library uses an instance of <tt>parser<type></tt> if the
+command line option specifies that it uses values of type '<tt>type</tt>'.
+Because of this, custom option processing is specified with specializations of
+the '<tt>parser</tt>' class.</p>
+
+<p>The CommandLine library provides the following builtin parser
+specializations, which are sufficient for most applications. It can, however,
+also be extended to work with new data types and new ways of interpreting the
+same data. See the <a href="#customparser">Writing a Custom Parser</a> for more
+details on this type of library extension.</p>
+
+<ul>
+
+<li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a>
+can be used to map strings values to any data type, through the use of the <a
+href="#cl::values">cl::values</a> property, which specifies the mapping
+information. The most common use of this parser is for parsing enum values,
+which allows you to use the CommandLine library for all of the error checking to
+make sure that only valid enum values are specified (as opposed to accepting
+arbitrary strings). Despite this, however, the generic parser class can be used
+for any data type.</li>
+
+<li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a>
+is used to convert boolean strings to a boolean value. Currently accepted
+strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>",
+"<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li>
+
+<li><a name="stringparser">The <b><tt>parser<string></tt>
+specialization</b></a> simply stores the parsed string into the string value
+specified. No conversion or modification of the data is performed.</li>
+
+<li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a>
+uses the C <tt>strtol</tt> function to parse the string input. As such, it will
+accept a decimal number (with an optional '+' or '-' prefix) which must start
+with a non-zero digit. It accepts octal numbers, which are identified with a
+'<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of
+'<tt>0x</tt>' or '<tt>0X</tt>'.</li>
+
+<li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and
+<b><tt>parser<float></tt> specializations</b> use the standard C
+<tt>strtod</tt> function to convert floating point strings into floating point
+values. As such, a broad range of string formats is supported, including
+exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales.
+</li>
+
+</ul>
+
+</div>