Make meaning of parentheses for regex explicit in URL Pattern API (#3…

…5571)

files/en-us/web/api/url_pattern_api/index.md

@@ -27,7 +27,8 @@ can contain:
 - Non-capturing groups (`/books{/old}?`) which make parts of a pattern optional
   or be matched multiple times.
 - {{jsxref("RegExp")}} groups (`/books/(\\d+)`) which make arbitrarily complex
-  regex matches with a few [limitations](#regex_matchers_limitations).
+  regex matches with a few [limitations](#regex_matchers_limitations). _Note that the
+  parentheses are not part of the regex but instead define their contents as a regex._
 
 You can find details about the syntax in the [pattern syntax](#pattern_syntax)
 section below.
@@ -79,9 +80,9 @@ match the shortest possible string.
 ### Regex matchers
 
 Instead of using the default match rules for a group, you can use a regex for
-each group. This regex defines the matching rules for the group. Below is an
-example of a regex matcher on a named group that constrains the group to only
-match if it contains one or more digits:
+each group by including a regex in parentheses. This regex defines the matching
+rules for the group. Below is an example of a regex matcher on a named group
+that constrains the group to only match if it contains one or more digits:
 
 ```js
 const pattern = new URLPattern("/books/:id(\\d+)", "https://example.com");