ConTeXt XML: Configureable Titleblock

If the document has only one title and one author, you can use xmlfilter to filter out that information before flushing the rest of the content. For example:

\startbuffer[test]
<?xml version='1.0' standalone='yes?>
<document>
<title>The Title</title>
<author>The author</author>
<p>This is a first sentence</p>
</document>
\stopbuffer

\startxmlsetups xml:setup
  \xmlsetsetup{\xmldocument}{*}{-}
  \xmlsetsetup{\xmldocument}{document|p}{xml:*}
\stopxmlsetups

\xmlregistersetup{xml:setup}

\startxmlsetups xml:document
  \xmlfilter{#1}{/title/command(xml:title)}
  \xmlfilter{#1}{/author/command(xml:author)}
  \startdocument
  \xmlflush{#1}
  \stopdocument
\stopxmlsetups

\startxmlsetups xml:title
  \setupdocument[title={\xmlflush{#1}}]
\stopxmlsetups

\startxmlsetups xml:author
  \setupdocument[author={\xmlflush{#1}}]
\stopxmlsetups

\startxmlsetups xml:p
  \xmlflush{#1}\par
\stopxmlsetups

\startsetups document:start
  \startalignment[middle]
    {\ssbfa\setupinterlinespace
     \documentvariable{title}\endgraf}
     \blank[medium]
     \documentvariable{author}
   \stopalignment
   \blank[big]
\stopsetups

\xmlprocessbuffer{main}{test}{}

which gives

With this approach, it doesn't matter where the <title> and <author> block appear. For example, the following will also work:

\startbuffer[test]
<?xml version='1.0' standalone='yes?>
<document>
<p>This is a first sentence</p>
<title>The Title</title>
<author>The author</author>
</document>
\stopbuffer