Adding Dynamic Field Validation in Service Catalog

Hello expers, 
I want to know, how could i add validation on user selection fields in Service Catalog? 
i mean that for example, when we add a "text" as user selection and select type as "Number", we have only :
1-Greater than / Greater than or equal
2-Less than / Less than or equal 
what i need to know how to add more validation on that number for example: 
1-The Number should be 10 digits 
2-the number should start with specific digits.
Appreciate your cooperations, Thanks in advance.