问题
For example it works:
{<div\s+class=\"article\"><h2(.*)</div>}s
If I do this way, I get nothing:
{<div\s+class=\"article\">
<h2(.*)
</div>}s
I suspect that I should use some modifier, but I know which one from here: http://php.net/manual/en/reference.pcre.pattern.modifiers.php
回答1:
That would be the /x modifier:
x (PCRE_EXTENDED)
If this modifier is set, whitespace data characters in the pattern are totally ignored except when escaped or inside a character class, and characters between an unescaped # outside a character class and the next newline character, inclusive, are also ignored. This is equivalent to Perl's /x modifier, and makes it possible to include comments inside complicated patterns. Note, however, that this applies only to data characters. Whitespace characters may never appear within special character sequences in a pattern, for example within the sequence (?( which introduces a conditional subpattern.
It also allows commenting the pattern, which is extremely useful:
{<div\s+class=\"article\"> # many spaces between the div and the attribute
<h2(.*) # don't really care about closing the tag
</div>}sx
来源：https://stackoverflow.com/questions/7512781/php-regexp-how-to-use-newline-in-expression