Add better explanation for '^' in patterns

goggles/quickstart.goggle

@@ -37,9 +37,35 @@
 /this/is/*/pattern
 
 ! The special character '^' can be used to indicate that an URL delimiter such
-! as '/' or end-of-url can be matched (note: the number of carets allowed in a
-! given instruction is limited):
+! as '/' or end-of-url can be matched. More specifically, '^' is equivalent to
+! the regexp: [^\w\d._%-]|$
+!
+! This means that it can match either the end of the URL or any character that is
+! not a letter, digit, dot, underscore, percent sign or dash. Here are a few
+! examples of characters that are matched by '^': / (slash), = (equal),
+! [ (bracket), : (colon), etc.
+!
+! In practice, you will usually want to use '/' (or any other specific
+! separator like '=' or '?') most of the time in your patterns, except at the end
+! of a pattern in cases where you want to be a little bit more generic, and
+! express that your pattern should be either matching at the end of the URL or be
+! followed by a separator and then arbitrary URL components.
+!
+! For example, |https://example.org^ will match: 'https://example.org',
+! 'https://example.org/' or 'https://example.org/path'; but it will *not* match
+! 'https://example.org.ac', which is also a valid domain name starting with
+! 'https://example.org'.
+!
+! Another example, /foo.js^ will match: 'https://example.org/foo.js',
+! 'https://example.org/foo.js?param=42', 'https://example.org/foo.js/' but it
+! will *not* match 'https://example.org/foo.jsx' (because it is not followed by a
+! separator).
+!
+! Also note that the maximum number of carets allowed in a given instruction is
+! limited.
 /this/is/a/pattern^
+|https://example.org^
+/foo.js^
 
 ! By default, a pattern can match anywhere in the URL, but there are specific
 ! characters which can be used to indicate prefix or suffix matches: we call them