docs: move quirks to own file

QUIRKS.md

@@ -0,0 +1,13 @@
+# Quirks & Irregularities
+Syntax choices that make the grammar hard to parse and represent as AST in a
+way that is easy to maintain:
+
+- `d2:relationshipCount` is the only function expecting a quoted `UID`
+- a `programRuleStringVariableName` is any string and only identifiable having
+  a special meaning by its position as argument to certain functions
+- `PS_EVENTDATE:` is a tag for a `UID` for a dataResolver value but does not use the
+  `#{...}` wrapper and can therefore easily be confused for a named function
+- functions accepting dataResolver item values do not accept all dataResolver item value types
+  that can occur on top level.
+- the `de:*`-functions contain `:` which is hard to distinguish from a tag
+- `orgUnit.*`-functions contain `.` which is hard to distinguish from a method

README.md

@@ -43,18 +43,4 @@ To select which expression is used the `Expression` is parameterized with a `Mod
 * `INDICATOR_EXPRESSION`: Computes a number for an indicator expression (ad-hoc aggregate data computation)
 * `PROGRAM_INDICATOR_EXPRESSION`: Computes a number for a program indicator expression (persisted aggregate data computation)
 * `RULE_ENGINE_CONDITION`: Computes a boolean to check if a rule applies
-* `RULE_ENGINE_ACTION`: Computes a boolean, string, number or date from a rule
-
-### Quirks & Irregularities
-Syntax choices that make the grammar hard to parse and represent as AST in a
-way that is easy to maintain:
-
-- `d2:relationshipCount` is the only function expecting a quoted `UID`
-- a `programRuleStringVariableName` is any string and only identifiable having
-  a special meaning by its position as argument to certain functions
-- `PS_EVENTDATE:` is a tag for a `UID` for a dataResolver value but does not use the
-  `#{...}` wrapper and can therefore easily be confused for a named function
-- functions accepting dataResolver item values do not accept all dataResolver item value types
-  that can occur on top level.
-- the `de:*`-functions contain `:` which is hard to distinguish from a tag
-- `orgUnit.*`-functions contain `.` which is hard to distinguish from a method
+* `RULE_ENGINE_ACTION`: Computes a boolean, string, number or date from a rule