In that case the answer is easy - switch to using Perl then you take advantage of the resources provided by PerlMonks.

Perhaps if you showed us the change you made we could see what you did wrong. At a random shout in the dark you inserted stuff inside the recursive part of the pattern. PCRE now supports the reusable sub-expression syntax.

The problem of matched parentheses is the most commonly quoted example of using this construct.

my $bal = qr/
    (?<bal>            # Name the rule (optional)  
    \{                 # Open brace
    (?>                # Possessive subgroup
        (?> [^{}]+ )   #  Grab all the non braces
    |                  #    or
        (?&bal)        #  Recurse
    )*                 # Zero or more times
    \}                 # Close brace
    )                  # End named rule
/x;

if ('{x{x}y{x}x}' =~ /^$bal$/ ){
    print "It's balanced\n";
}

$_= 'XXXX function xxx() {x{x}y{x}x} XXXX';

while ( /\bfunction\s+(\w+)\(\)\s*($bal)/g ){
    print "function: $1\nbody: $2\n";
}
[download]

This, of course, is Perl code - adapting it to PHP is left as a exercise for the reader.

I should add, this only checks for nested {} it doesn't know to ignore {} within quotes - that too is possible by hybridising the above with the tricks for parsing CSV.