Improve documentation of Tags_format, add a few backlinks, see #887

Docs/Tags_format.md

@@ -4,6 +4,8 @@ Tags format
 When creating the `json` file describing your layer or theme, you'll have to add a few tags to describe what you want.
 This document gives an overview of what every expression means and how it behaves in edge cases.
 
+If the schema-files note a type `string | AndOrTagConfigJson`, you can use one of these values.
+
 Strict equality
 ---------------
 
@@ -38,8 +40,8 @@ If `key` is not present or empty, this will match too.
 This implies that, to check if a key is present, `key!=` can be used. This will only match if the key is present and not
 empty.
 
-Number comparison
+Number and date comparison
------------------
+--------------------------
 
 If the value of a tag is a number (e.g. `key=42`), one can use a filter `key<=42`, `key>=35`, `key>40` or `key<50` to
 match this, e.g. in conditions for renderings. These tags cannot be used to generate an answer nor can they be used to
@@ -51,6 +53,8 @@ special circumstances (e.g. `surface_area=42 m2` or `length=100 feet`), this wil
 values (`surface=422` or if a length in meters is compared to). However, this can be partially alleviated by using '
 Units' to rewrite to a default format.
 
+Dates can be compared with the same expression: `somekey<2022-06-22` will match if `somekey` is a date and is smaller then 22nd june '22.
+
 Regex equals
 ------------
 
@@ -87,7 +91,7 @@ To mitigate this, use:
 {
     "mappings": [
         {
-            "if":"key:={some_other_key}"
+            "if":"key:={some_other_key}",
             "then": "...",
             "hideInAnswer": "some_other_key="
         }

Logic/Tags/TagUtils.ts

@@ -182,6 +182,7 @@ export class TagUtils {
 
     /**
      * Returns wether or not a keys is (probably) a valid key.
+     * See 'Tags_format.md' for an overview of what every tag does
      *
      * // should accept common keys
      * TagUtils.isValidKey("name") // => true

Models/ThemeConfig/Json/TagConfigJson.ts

@@ -1,3 +1,8 @@
+/**
+ * A small interface to combine tags and tagsfilters.
+ * 
+ * See https://github.com/pietervdvn/MapComplete/blob/develop/Docs/Tags_format.md for documentation
+ */
 export interface AndOrTagConfigJson {
     and?: (string | AndOrTagConfigJson)[]
     or?: (string | AndOrTagConfigJson)[]