Add section about OQL syntax basics

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.
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-## Reserved Words {#reserved-oql-words}
+## Syntax basics
+
+An OQL statement consists of [keywords](#reserved-oql-words), identifiers, [value literals](/refguide/oql-expression-syntax/#oql-literals) and [operators](/refguide/oql-expression-syntax/#oql-operators).
+
+Identifiers are used for module, entity, attribute, association, and alias names and parts of names in paths. Identifiers 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 allow special characters `.`, `/`, and `@`.
+
+Multiple identifiers can be composed into a path, separated by special characters `.` and `/`. The `.` special character can be used to indicate the module and entity in the form `Module.Entity`. The `/` special character can be used to indicate the attribute of an entity in the form `Module.Entity/Attribute` and it can be used for separating associations in long paths. Examples of paths can be seen in the [Select from Multiple Tables using JOIN](/refguide/oql-clauses/#join) section of *OQL Clauses*.
+
+### 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`.
 
@@ -85,5 +93,5 @@ In OQL, `FLOAT` is a reserved word for legacy reasons. Mendix no longer supports
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-In OQL, `DELETE`, `INSERT`, `REPLACE`, `UPDATE`, `UPSERT`, `INTO`, `SET`, `VALUES`, `IGNORE`, `MATCHED`, `DUPLICATE`, `KEY`, `CONFLICT`, `MERGE`, `USING`, `SOURCE`, `TARGET`, and `WITH` are reserved but not yet used.
+In OQL, `REPLACE`, `UPSERT`, `SET`, `VALUES`, `IGNORE`, `MATCHED`, `DUPLICATE`, `KEY`, `CONFLICT`, `MERGE`, `USING`, `SOURCE`, `TARGET`, and `WITH` are reserved but not yet used.
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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.