reference to undeclared namespace prefix:'xsl'

hi, I am using xmlspy 3.5 for processing my xsl style sheet. I want to use
inside this style sheet the following entity:

-------------------------------
<!---demo.xsl-->
<!DOCTYPE xsl:stylesheet [
<!ENTITY ntilde "<xsl:text>&#241;</xsl:text>">
]>
<xsl:stylesheet....
------------------------------

now, when I try to transform my xml file, I get the following error:
"reference to undeclared namespace prefix:'xsl' in file demo.xsl"

as far as I understand xsl, the entity should be substituted inside my
stylesheet whenever I use &ntilde; but it seems as if the xsl engine tries
to use <xsl:text> before knowing the xsl-namespace.
so, what is wrong? can I not use any xsl-elements (as <xsl:text above)
before declaring the xsl-namespace?
I saw a lot examples in the internet doing the same thing as I want to do.
but mine does simply not work.
can anybody help me?
thx in advance, stefan



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