Is substring -before cyclic in nature?

Hi,

I am using substring-before on

<tag>Value is 10</tag>
<tag>This Value is 10</tag>
<tag>Check for Value</tag>

like this - 
substring-before(.,'Value')

In the first case
<tag>Value is 10</tag>

I am getting the result as - Value is 10
I am expecting to get nothing here.
Does substring-before behave cyclic if the
value is found at the start of the string?

Thanks in advance.

________________________________________________________________________
Missed your favourite TV serial last night? Try the new, Yahoo! TV.
       visit http://in.tv.yahoo.com

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list