settings: Fix/clarify %variable escaping

Author: sirainen

docs/core/settings/types.md

@@ -59,10 +59,6 @@ dovecotlinks:
 
 String can contain any character. Strings support [[variable]].
 
-::: tip
-If you need the `%` character verbatim you have to escape it as `%%`.
-:::
-
 ## String without variables
 
 Certain settings require specific variables and thus don't use the default

docs/core/settings/variables.md

@@ -53,7 +53,11 @@ Filters can accept parameters, both positional and named. E.g. `%{literal('\r\n\
 to CR LF. `%{user | substr(0, 1)}` will take first character of username. Example of named parameters
 would be `%{user | md5(rounds=1000,salt='pepper')}`
 
-You can use `%%{variable}` to escape this, and emit `%{variable}`.
+For escaping:
+ * `%%{text}` emits `%{text}`
+ * `%%%{text}` emits `%%{text}`
+ * `%{concat('%', variable)}` emits `%<expanded variable>`
+ * Otherwise `%` doesn't need any escaping. `%%` emits the same `%%`.
 
 Filters accept strings, numbers and variables as parameters. Parameters can be positional or
 named key-value pairs. Key names cannot be variables.