Finally I saw the problem. Calling \xmlfilter{#1}{./node/command(demo:attribute:node)} is the right way.
Sorry for the noise.

dr. Hans van der Meer
> On 30 Aug 2023, at 13:49, Hans van der Meer via ntg-context <ntg-context@ntg.nl> wrote:
> 
> This line of code comes from the xml documentation (page 31):
> \xmlfilter{#1}{./node[@type=="cleanup"]}
> It should select among the <node>'s those with <node type="cleanup">.
> However, this node is not selected in the call to \xmlfilter.
> Where am I wrong?
> 
> MWE follows
> 
> 
> % failure to typeset attribute selected.
> \setuppapersize[A5][A5]
> \startxmlsetups demo:attribute
> 	\xmlsetsetup{#1}{root|node}{demo:attribute:*}
> \stopxmlsetups
> \xmlregisterdocumentsetup{demo}{demo:attribute}
> \startxmlsetups demo:attribute:root
> 	Execute \type{\xmlall{#1}{./node}}
> 		\crlf
> 		\xmlall{#1}{./node}
> 		\crlf
> 	Execute \type{\xmlfilter{#1}{./node[@type=="cleanup"]}}
> 		\xmlfilter{#1}{./node[@type=="cleanup"]}
> 		\crlf
> \stopxmlsetups
> \startxmlsetups demo:attribute:node
> 	calling node <\xmltag{#1}>
> 	\xmlflush{#1}
> 	\crlf
> \stopxmlsetups
> \startbuffer[attribute]
> <root>
> <node>no attribute</node>
> <node type="cleanup">attribute type = cleanup</node>
> </root>
> \stopbuffer
> \startbuffer[attribute2]
> <root>
> <node>no attribute</node>
> <node type="cleanup">attribute type=cleanup</node>
> </root>
> \stopbuffer
> \starttext
> \ConTeXt\ version\contextversion\blank
> \xmlprocessbuffer{demo}{attribute}{}
> \stoptext
> 
> <xml-tex-attribute-select.pdf>
> 
> 
> Hans van der Meer
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