[xsl] text() function

["Sameer N" <samooo_vc@xxxxxxxxxxx>]

I was reading this blog 
http://blog.parthenoncomputing.com/dbxml/archives/2005/02/faq_how_do_i_ge_1.html 
and am confused here.

I am trying to look if the word blah exists in the entire document.

Is there any difference between
//*[conatins(text(), "blah")]
and
//*[conatins( . , "blah")]

Is there any difference between the performance of the above two??
Is the using of string() function as suggested in the blog right way to do 
what I want... because I read in one book that string() only matches the 
first element found and does not go thru the entire document trying to match 
all elements found.

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