13.2.11 Cloisters

The location between the ? and the : of a non-capturing cluster is called a cloister.(8) You can put modifiers there that will cause the enclustered subpattern to be treated specially. The modifier i causes the subpattern to match case-insensitively:

(pregexp-match "(?i:hearth)" "HeartH") ⇒ ("HeartH")

The modifier x causes the subpattern to match space-insensitively, ie, spaces and comments within the subpattern are ignored. Comments are introduced as usual with a semicolon (;) and extend till the end of the line. If you need to include a literal space or semicolon in a space-insensitized subpattern, escape it with a backslash.

(pregexp-match "(?x: a   lot)" "alot")
 ⇒ ("alot")

(pregexp-match "(?x: a  \\  lot)" "a lot")
 ⇒ ("a lot")

(pregexp-match "(?x:
   a \\ man  \\; \\   # ignore
   a \\ plan \\; \\   # me
   a \\ canal         # completely
   )" 
 "a man; a plan; a canal")
 ⇒ ("a man; a plan; a canal")

You can put more than one modifier in the cloister.

(pregexp-match "(?ix:
   a \\ man  \\; \\   # ignore
   a \\ plan \\; \\   # me
   a \\ canal         # completely
   )" 
 "A Man; a Plan; a Canal")
 ⇒ ("A Man; a Plan; a Canal")

A minus sign before a modifier inverts its meaning. Thus, you can use -i and -x in a subcluster to overturn the insensitivities caused by an enclosing cluster.

(pregexp-match "(?i:the (?-i:TeX)book)"
  "The TeXbook")
 ⇒ ("The TeXbook")

This regexp will allow any casing for the and book but insists that TeX not be differently cased.

This document was generated on March 31, 2014 using texi2html 5.0.