preg_replace « String « PHP

1.$0 is set to the whole match, then $1, $2
2.Converting Line Breaks
5.preg_replace with index
6.Pass a fourth parameter to preg_replace( ) to specify the maximum number of replacements you want to make.
7.Pass arrays of regular expressions and replacement strings to preg_replace().
8.Replacing with preg_replace()
9.Using Back References with preg_replace()

10.Using preg_replace() to Replace Patterns
11.e modifier treats the replacement string in preg_replace() as if it were PHP.
12.pass arrays as parameter one and parameter two, and preg_replace() performs multiple replaces
13.Escape a > character in HTML
14.Replacing URLs with Links
15.Formatting a Phone Number
16.Entity encoding matched text
17.Escaping Special Characters
18.Regular Expression Replacements
19.Remove any doubled-up whitespace
20.Replace any non-space whitespace, with a space
21.Replace with regular expression
22.Replacing using backreferences
23.Quote escaping in backreference replacements