# Using expressions in EMX

## Introduction

For some entity type attributes an expression can be set that determines whether or not a condition is true based on the attribute values to determine whether values are valid, visible or required.

### Examples

The following expression returns true when the value of attribute 'myAttributeName' of an entity only contains alphanumberic characters:

```javascript
regex('^[a-zA-Z0-9]+$',{myStringAttributeName})
```

In this example:

* `{myStringAttributeName}` looks up the value of the `myStringAttributeName` variable
* `regex` is a function

You can combine expressions to perform more complex logic:

```
{myIntAttributeName} > 3 and {myIntAttributeName} < 6
```

### Reference

See [molgenis/molgenis-expressions](https://github.com/molgenis/molgenis-expressions#readme) for a complete description of the syntax.


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