Hello Sushma, 

It is possible to use regExp for igTextEditor input validation.

What is required is to specify the validatorOptions and include the expression as well. For example, initializing igTextEditor with validatorOptions will look like the following: 

            $("#textEditor").igTextEditor({      
                validatorOptions:{
                required : true,
                keepFocus: "once",
                regExp : "^[0-9]+$",
                width: 195
              }
         });

You could observe a sample with this regExp and the expected behavior here

As various igEditors depend on the igValidator widget, you could find it’s API here:
http://help.infragistics.com/jQuery/2015.1/ui.igvalidator#options:regExp 

What is more, there are a couple of online samples regarding validation to be found at our IgniteUI site.
For example: http://igniteui.com/editors/validation . In this sample, during the initialization a function is set for validationOptions: getValidationOptions(). This shows the flexibility to provide these options on later stage, depending on some specific conditions. 

In case you are using a different version of IgniteUI where the regExp validation is not working as expected, please let me know so we could take the necessary steps.