problem with ' in when sentence

Hello.
I need to create an XSLT file that contains the following "when" sentence:

<xsl:when test="self::node()[@content=' ' ']"> 
</xsl:when>

The problem is that generates an error, the character ' is not correct for the attribute value. Is there a chain of escape for the possible introduction of the ' without me for a mistake?

Thanks 



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