Add section about OQL syntax basics

Author: pijuskri

content/en/docs/refguide/modeling/domain-model/oql/_index.md

@@ -28,7 +28,15 @@ OQL queries do not take security into account out-of-the-box. This means that yo
 You can try your OQL example online in the [OQL Playground](https://service.mendixcloud.com/p/OQL) demo app.
 {{% /alert %}} 
 
-## Reserved Words {#reserved-oql-words}
+## Syntax basics
+
+An OQL statement is made of [keywords](#reserved-oql-words), identifiers, [value literals](#oql-literals) and [operators](#oql-operators).
+
+Identifiers are used for module, entity, attribute, association, alias names and parts of names in paths. Identifiers parts are only allowed to contain latin characters(`a-Z`), underscores(`_`) and numbers(`0-9`). Numbers can not be used as for the first character of an identifier. Identifiers can be wrapped in double quotes `" "` to also allow special characters `.`, `/`, `@`. An example 
+
+Multiple identifiers can be composed into a path, separated by special characters `.` and `/`. Both special characters can be used for indicating the module or attribute of an entity in the form `Module.Entity.Attribute` in OQL queries. In OQL statements, only the `.` special character can be used to indicate the statement entity. Both special characters can be used for separating associations in long paths. Examples of paths can be seen in the [OQL clauses](#longpath) page.
+
+### Reserved Words {#reserved-oql-words}
 
 Words with a specific purpose in OQL are reserved. If you use reserved words for entity, variable, or attribute names in an OQL query, they must be wrapped in double quotes `" "`. For example, in the OQL query `SELECT AVG(TotalPrice) FROM Sales."Order" WHERE IsPaid = 1`, `Order` needs to be wrapped in quotes because it is a reserved word, as it can be used to `ORDER BY`.
 

content/en/docs/refguide/modeling/domain-model/oql/oql-expression-syntax.md

@@ -42,7 +42,7 @@ OQL supports a set of data types that differ slightly from [Mendix data types](/
 | `LONG`     | Integer/Long     | 5                     | 64 bit width integer data                  |
 | `STRING`   | String           | 'my_string'           | Textual data                               |
 
-## Literals
+## Literals {#oql-literals}
 
 Literals represent values that are constant and are part of the query itself. The supported literals are detailed below:
 
@@ -120,7 +120,7 @@ FROM
 	Sales.Person
 ```
 
-## Operators
+## Operators {#oql-operators}
 
 Operators perform common operations and, unlike functions, do not put their parameters in parentheses. They take `expression` as input, which can be other operator results, functions, columns and literals.