Check if a text string is a number

To check whether a text string is a number, ie whether it contains only valid number characters, you can use the following syntax with the IsNumber function:

IsNumber(<text value>)
<text value> is a number

For example, to check that an identification number contains only valid number characters, you would write the following rule:

the identification number is valid if

the identification number is a number

The text value may be a text attribute, text constant or any expression that returns a text constant.

TIP: any valid number characters may be present in the text string, eg minus sign, decimal point, etc.