If the pattern contains subexpressions in parentheses, the replacement argument may
contain a special code for specifying which subexpression to replace. The form is to use
two backslashes followed by a single digit, zero through nine. Zero matches the entire
expression; one through nine each match the first nine subexpressions, respectively.
Subexpressions are numbered left to right, which accounts for nested subexpressions.
Regular expressions are discussed in depth in Chapter 16.
Figure 9-11. ereg_replace.boolean eregi(string pattern, string text, array matches)
The eregi function operates identically to ereg with the exception that letters are
matched with no regard for upper or lower case.
Regular expressions are discussed in depth in Chapter 16.
string eregi_replace(string pattern, string replacement, string
text)