$re = '/((?:^|[^\\\\\n])(?:\\\\{2})*)\{([#$&])([\w.]+)(?::([^}\\\\]*(?:\\\\.[^}\\\\]*)*))?}/m';
$str = '{&var} --> Variable stored in a dictionary --> dict("var")
{$prop} --> Property of a class cls.prop read by CallByName and PropGet
{#const} --> Some constant values by name from a function
Value of foo is \'{&var:DD.MM.YYYY}\' and bar is \'{$prop}\'
Value of foo is \'{&var:DD.{MM}.YYYY}\' and bar is \'{$prop}\'
Value of foo is \'{&var:DD.\\{MM\\}.YYYY}\' and bar is \'{$prop}\'
This should not match \'\\{&var:DD.\\{MM\\}.YYYY\\}\' but this one \'{&var:DD.\\{MM\\}.YYYY}\'';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php