PHP regex delimiters, / vs. | vs. {} , what are the differences?

Question

In the PHP manual of PCRE, http://us.php.net/manual/en/pcre.examples.php, it gives 4 examples of valid patterns:

• /<\\/\\w+>/

Answer 1

In fact you can use any non alphanumeric delimiter (excluding whitespaces and backslashes)

"%^[a-z]%"

works as well as

"*^[a-z]*"

as well as

"!^[a-z]!"

Answer 2

No difference, except the closing delimiter cannot appear without escaping.

This is useful when the standard delimiter is used a lot, e.g. instead of

preg_match("/^http:\\/\\/.+/", $str);

you can write

preg_match("[^http://.+]", $str);

to avoid needing to escape the /.