The regular expression is generated in the notation used by awk, ed, egrep, Emacs, expect, find, grep, lex, Lisp, MySQL, OpenOffice.org, Perl, PHP, PostgreSQL, Procmail, Python, Sed, Tcl, VBscript, Vi, and Vim.
The Minix operating system, among others, uses a clone of nroff called cawf by Vic Abell, based on awf, the Amazingly Workable Formatter designed in awk by Henry Spencer.