camelCase

^[a-z][a-zA-Z0-9]*$

PascalCase or UpperCamelCase

^[A-Z]+[a-zA-Z0-9]*$

PascalCase or UpperCamelCase starting with letter I

^I[A-Z]+[a-zA-Z0-9]*$

UpperCase separated by _

^[A-Z][A-Z0-9]*(_[A-Z0-9]+)*$