[Ruleset Engine, Rules] Clarify function usage (cloudflare#25050)

Author: pedrosousa

src/content/docs/rules/transform/url-rewrite/reference/fields-functions.mdx

@@ -28,4 +28,4 @@ A rewrite expression (that is, the expression that defines the dynamic URL rewri
 
 Refer to the [Fields reference](/ruleset-engine/rules-language/fields/reference/) for more information on these fields.
 
-The [`concat()`](/ruleset-engine/rules-language/functions/#concat), [`regex_replace()`](/ruleset-engine/rules-language/functions/#regex_replace), and [`wildcard_replace()`](/ruleset-engine/rules-language/functions/#wildcard_replace) functions can appear only **once** in a rewrite expression.
+The [`concat()`](/ruleset-engine/rules-language/functions/#concat), [`regex_replace()`](/ruleset-engine/rules-language/functions/#regex_replace), and [`wildcard_replace()`](/ruleset-engine/rules-language/functions/#wildcard_replace) functions can appear only once in a rewrite expression. Additionally, you cannot nest the `regex_replace()` and `wildcard_replace()` functions.

src/content/docs/ruleset-engine/rules-language/functions.mdx

@@ -249,8 +249,10 @@ Examples:
 
 Create capture groups by putting part of the regular expression in parentheses. Then, reference a capture group using `${<NUMBER>}` in the replacement string, where `<NUMBER>` is the number of the capture group.
 
+You can only use the `regex_replace()` function once in an expression, and you cannot nest it with the [`wildcard_replace()`](/ruleset-engine/rules-language/functions/#wildcard_replace) function.
+
 :::note
-You can only use the `regex_replace()` function in rewrite expressions of [Transform Rules](/rules/transform/) and target URL expressions of [dynamic URL redirects](/rules/url-forwarding/single-redirects/).
+Currently, the `regex_replace()` function is only available in rewrite expressions of [Transform Rules](/rules/transform/) and target URL expressions of [dynamic URL redirects](/rules/url-forwarding/single-redirects/).
 :::
 
 ### `remove_bytes`
@@ -423,6 +425,8 @@ To perform case-sensitive wildcard matching, set the `flags` parameter to `"s"`.
 
 This function uses lazy matching, that is, it tries to match each `*` metacharacter with the shortest possible string.
 
+You can only use the `wildcard_replace()` function once in an expression, and you cannot nest it with the [`regex_replace()`](/ruleset-engine/rules-language/functions/#regex_replace) function.
+
 Examples:
 
 - If the full URI is `https://apps.example.com/calendar/admin?expand=true`,<br/>