'''Tcl Regular Expression Match Requirements'''  describes a set of [regular
expressions], and what, ideally, they would match.



** Description **

Tcl's regular expression engine has a particular design that leads to some
unexpected results.  The collection below of regular expression applications on
this page and their ideal results is intended as a guide for the further
development of regular expression routines in Tcl.




** `(t*?)?` **

Ideal:

======
% regexp -inline -indices {(t*?)?} ttt
{0 -1} {0 -1}
======

Actual:

======
% regexp -inline -indices {(t*?)?} ttt
{0 2} {0 2}
======



** `.*(a*){1,3}?` **

Ideal and actual:

======
regexp -indices -inline {.*(a*){1,3}?} aaaa
{0 3} {4 3}
======



** `(a.*?f)*` **

If there is a quantifier on a capturing expression, it should return a list of
matches:

======
% regexp -indices -inline {(a.*?f)*} aaafaaafjkl
{0 7} {{0 3} {4 7}}
======

Actual:

======
% regexp -indices -inline {(a.*?f)*} aaafaaafjkl
{0 7} {4 7}
======




<<categories>> regular expressions