Nice link! Does a pretty good job at demonstating things. While some of the examples could be improved, overall, it looks pretty good.
There is one thing to note that I spotted:
In order to be taken literally, you must escape the characters ".[$()|*+?{\" with a backslash ('\'), as
they have special meaning.
You don't actually need to escape { or } characters as a rule (there are some odd exceptions). I think the reason why people think these must always be escaped is because they are used in intervals for example: \d{2,3}. But for most intents and purposes, these don't need to be escaped.
consider:
$str = 'dhjd{{{{{dskdj';
preg_match('#{{2,}#', $str, $match);
echo $match[0]; // Output: {{{{{
In fact, even when using { and } as delimiters, you can get away with not escaping { or } within those delimiters (on the condition that you have matching sets of { and } inside your pattern...)
$str = 'dhk d hkj {_GR_} hdksdhakj {_TY_} jksd!';
$str = preg_replace('{{_[^_]+_}}', '{_XX_}', $str);
echo $str; // Output: dhk d hkj {_XX_} hdksdhakj {_XX_} jksd!
Note that inside the { and } delimiters, there is a matching set of { and }. If you remove one or the other of those inner braces, you will either get a Unknown modifier '}' if the first is missing, or No ending matching delimiter '}' if the second is missing. In those cases, the lone mismatched one needs to be escaped, and even then, the results will not be what you expect.
Point being, in general, { and } are safe enough to not require escaping.
