1. Simple Validation
   required, email, phpone number , digtial-only, alphpbet-only,etc.
   These validation can be done using a regular expression.
   We cann’t do Date validation only using a regular expression, but I still prefer to consider it to be an Simple Validation.
2. Complex Validation
   length,range.
   These validation need extra argument to decide the result.
3. Mixed Validation
   Password-identical Validation, required-if-something validation,etc.
   The Validation results are based on more than one element.