r.
<B>Tcl_RegExpCompile</B> compiles a regular expression string into
the internal form used for efficient pattern matching.
The return value is a token for this compiled form, which can be
used in subsequent calls to <B>Tcl_RegExpExec</B> or <B>Tcl_RegExpRange</B>.
If an error occurs while compiling the regular expression then
<B>Tcl_RegExpCompile</B> returns NULL and leaves an error message
in the interpreter result.
Note:  the return value from <B>Tcl_RegExpCompile</B> is only valid
up to the next call t