Any valid regular expression could be used here. Some examples you can see below.
Since version 1.4.17 you can use the reserved word [unique] in order to check for field's value uniqueness. See examples below.
| Validation | Regular expression |
|---|---|
| Value is empty | ^\s*$ |
Value NOT matching something (Allow everything, but 'something'. Useful when you would like to apply validation on dropdown fields) | ^(?!something).*$ |
| Value is not empty | ^(?=\s*\S).*$ |
| Value is alphanumeric | ^[a-zA-Z0-9]*$ |
| Value contains only letters | ^[a-zA-Z]*$ |
| Value length (1-20 chars) | ^.{1,20}$ |
| Only numbers | ^[0-9,;]+$ |
| Checks if the field's value is unique within the dataset | [unique] |
| Checks if the field's value is unique within the dataset and ensures it's length (1-20 chars) | ^.{1,20}$[unique] |
| Allow only PDF files (files with "pdf" file extension) |