Add 'visit'-functionality to TagsFilter, add case invariant regextag

Docs/Tags_format.md

@@ -57,6 +57,9 @@ Regex equals
 A tag can also be tested against a regex with `key~regex`. Note that this regex __must match__ the entire value. If the
 value is allowed to appear anywhere as substring, use `key~.*regex.*`
 
+Regexes will match the newline character with `.` too - the `s`-flag is enabled by default.
+To enable case invariant matching, use `key~i~regex`
+
 Equivalently, `key!~regex` can be used if you _don't_ want to match the regex in order to appear.
 
 
@@ -81,13 +84,15 @@ which we do not want.
 To mitigate this, use:
 
 ```json
-"mappings": [
 {
-    "if":"key:={some_other_key}"
-    "then": "...",
-    "hideInAnswer": "some_other_key="
+    "mappings": [
+        {
+            "if":"key:={some_other_key}"
+            "then": "...",
+            "hideInAnswer": "some_other_key="
+        }
+    ]
 }
-]
 ```
 
 One can use `key!:=prefix-{other_key}-postfix` as well, to match if `key` is _not_ the same