I think it would be very interesting to see a survey of how deep XML
documents go in the wild. Except for pathological cases, I think they
would rarely go beyond 20 deep. Of course this will vary a great deal
by document type.

Ken, what does "quite deep" mean in your case?

<xsl:stylesheet
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  version="2.0">

<xsl:template match="/">
  <xsl:value-of
    select="max(//node()[not(node())]/count(ancestor::node()))"/>
</xsl:template>

  - XSLT       - 19
  - XSL-FO     - 24
  - UBL        - 20
  - Code Lists - 16

This is related to the rule of thumb that streaming will help with
memory management, but will not (perhaps contrary to expectations)
have much impact on processing speed.

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