How to Validate a TextBox with a Number & with a specific Text

Hi, I've a Textbox
I can enter a Number which is greaterThan "0" or I can enter text which is only "NUMEROUS"
so
If I enter 0 (or) negetive Number (or) any text other than "NUMEROUS", i must display error msg Like
"Don't Enter 0/Negetive No./text other than "NUMEROUS"
how to validate above situation
plz advice
 
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