Regular Expressions

Question

Hi,



Can you please explain me this regular expression?

(?!^[0-9]*$)(?!^[a-zA-Z]*$)^([a-zA-Z0-9]{8,10})$


[a-zA-Z0-9]{8,10} means any alphabets or digits 8 to 10 characters.

but

(?!^[0-9]*$) or  (?!^[a-zA-Z]*$)  what are these expressions?
 

Thanks in advance
Anand