Three curly brackets together in php source code

I just downloaded complete source code of PHP from php.net (PHP 5.4.0 [tar.bz2]). They are often using three curly brackets together as given below (The following code snippet extracted form ext/ctype/ctype.c.)

/* {{{ proto bool ctype_digit(mixed c)
   Checks for numeric character(s) */
 static PHP_FUNCTION(ctype_digit)
 {
  CTYPE(isdigit);
 }
/* }}} */

Does anyone have the idea why they are using these three curly brackets together?

Answer

They are vim fold markers, they make it easy to collapse and expand the text inbetween the triple curly braces in vim, in the example shown alternating between:

...

/* {{{ proto bool ctype_digit(mixed c)
   Checks for numeric character(s) */
static PHP_FUNCTION(ctype_digit)
{
    CTYPE(isdigit);
}
/* }}} */

...

and just

...

/* {{{ proto bool ctype_digit(mixed c)

...

If you look at the end of the file where you find them, you’ll often find a block like this:

/*
 * Local variables:
 * tab-width: 4
 * c-basic-offset: 4
 * End:
 * vim600: sw=4 ts=4 fdm=marker
 * vim<600: sw=4 ts=4
 */

Which is another more-obvious indicator that these comments relate to vim.