Author: Jeffrey E. F. Friedl
WWW book information:
More book information: http://enterprise.ic.gc.ca/~jfriedl/regex/ (found broken, 28 Feb 2008)
Author's Web site: http://regex.info/
This book explains regular expressions in general, and then covers a number of different tools explaining specialized variations. The book focuses more on Perl, but Tcl is one of the tools covered in its own special section. And more...
The second edition praises Tcl's regular expression engine: Henry's Tcl regex engine is an important step forward.
Also, in Chapter 6: Crafting an Efficient Expression, Friedl says: Most of what this chapter talks about simply does not apply to Tcl. And, as the sidebar explains, Henry Spencer's Tcl regex is a hybrid DFA/NFA engine and it doesn't need most of the optimizations described in the chapter.