Function to return specific text in source code

[Rigel]

I'm very new to javascript, and I wondered if there was a sample function that searched for specific text in a web page's source code delineated only by the text previous the start of the wanted string and the text after the wanted string. I also want to if there is a way to limit the text search to a specific area of the code, to enable the user to skip a lot of repeating text in order to find the text directly before the wanted string. Any help is greatly appreciated.