# WEM Expressions Reference

{% hint style="info" %}
**Unknown?**\
In general, a function, keyword or operator returns an `unknown` value if one or more parameters are unknown. Make sure to check for unknown situations using the appropriate functions (HasValue, IsEmpty, IsUnknown and the question mark)
{% endhint %}

{% hint style="info" %}
Most Text-related functions, keywords and operators are case-insensitive and ignore diacritics. You can find the Priority of operations [here.](https://docs.wem.io/platform/~/changes/y5gAfiyi2fILzrLzUUHj/wemtipsandtricks/tips-and-tricks/order-of-operators)
{% endhint %}

{% content-ref url="functions" %}
[functions](https://docs.wem.io/platform/~/changes/y5gAfiyi2fILzrLzUUHj/wemreference/functions)
{% endcontent-ref %}

{% content-ref url="keywords" %}
[keywords](https://docs.wem.io/platform/~/changes/y5gAfiyi2fILzrLzUUHj/wemreference/keywords)
{% endcontent-ref %}

{% content-ref url="operators" %}
[operators](https://docs.wem.io/platform/~/changes/y5gAfiyi2fILzrLzUUHj/wemreference/operators)
{% endcontent-ref %}

{% content-ref url="data-types" %}
[data-types](https://docs.wem.io/platform/~/changes/y5gAfiyi2fILzrLzUUHj/wemreference/data-types)
{% endcontent-ref %}

{% content-ref url="sql-compatibility" %}
[sql-compatibility](https://docs.wem.io/platform/~/changes/y5gAfiyi2fILzrLzUUHj/wemreference/sql-compatibility)
{% endcontent-ref %}

{% content-ref url="wem-widgets" %}
[wem-widgets](https://docs.wem.io/platform/~/changes/y5gAfiyi2fILzrLzUUHj/wemreference/wem-widgets)
{% endcontent-ref %}