Using an HTML entity in XSLT (e.g. )
XsltXslt Problem Overview
What is the best way to include an html entity in XSLT?
<xsl:template match="/a/node">
<xsl:value-of select="."/>
<xsl:text> </xsl:text>
</xsl:template>
this one returns a XsltParseError
Xslt Solutions
Solution 1 - Xslt
You can use CDATA section
<xsl:text disable-output-escaping="yes"><![CDATA[ ]]></xsl:text>
or you can describe in local DTD:
<!DOCTYPE xsl:stylesheet [ <!ENTITY nbsp " "> ]>
or just use   instead of
Solution 2 - Xslt
It is also possible to extend the approach from 2nd part of aku's answer and get all known character references available, like this:
<!DOCTYPE stylesheet [
<!ENTITY % w3centities-f PUBLIC "-//W3C//ENTITIES Combined Set//EN//XML"
"http://www.w3.org/2003/entities/2007/w3centities-f.ent">
%w3centities-f;
]>
...
<xsl:text> −30°</xsl:text>
There is certain difference in the result as compared to <xsl:text disable-output-escaping="yes"> approach. The latter one is going to produce string literals like for all kinds of output, even for <xsl:output method="text">, and this may happen to be different from what you might wish... On the contrary, getting entities defined for XSLT template via <!DOCTYPE ... <!ENTITY ... will always produce output consistent with your xsl:output settings.
It may be wise then to use a local entity resolver to keep the XSLT engine from fetching character entity definitions from the Internet. JAXP or explicit Xalan-J users may need a patch for Xalan-J to use the resolver correctly. See my blog http://s-n-ushakov.blogspot.com/2011/09/xslt-entities-java-xalan.html">XSLT, entities, Java, Xalan... for patch download and comments.
Solution 3 - Xslt
one other possibility to use html entities from within xslt is the following one:
<xsl:text disable-output-escaping="yes">&nbsp;</xsl:text>
Solution 4 - Xslt
> this one returns a XsltParseError
Yes, and the reason for that is that is not a predefined entity in XML or XSLT as it is in HTML.
You could just use the unicode character which stands for:  
Solution 5 - Xslt
XSLT only handles the five basic entities by default: lt, gt, apos, quot, and amp. All others need to be defined as @Aku mentions.
Solution 6 - Xslt
Now that there's Unicode, it's generally counter-productive to use named character entities. I would recommend using the Unicode character for a non-breaking space instead of an entity, just for that reason. Alternatively, you could use the entity  , instead of the named entity. Using named entities makes your XML dependent on an inline or external DTD.
Solution 7 - Xslt
I found all of these solutions produced a  character in the blank space.
Using <xsl:text> </xsl:text> solved the problem for me; but <xsl:text>#x20;</xsl:text> might work as well.
Solution 8 - Xslt
Thank you for your information. I have written a short blog post based on what worked for me as I was doing XSLT transformation in a template of the Dynamicweb CMS.
The blog post is here: How to add entities to XSLT templates.
/Sten Hougaard
Solution 9 - Xslt
It is necessary to use the entity #x160;
Solution 10 - Xslt
I had no luck with the DOCTYPE approach from Aku.
What worked for me in MSXML transforms on an Windows 2003 server, was
<xsl:text disable-output-escaping="yes">&#160;</xsl:text>
Sort of a hybrid of the above. Thanks Stackoverflow contributors!
Solution 11 - Xslt
One space character between text tags should be enough.