Can't get scheme handler to work.
Seems it gets never called. Instead I get:

Sablotron error on line 1: unknown encoding ''

Example script:

<?php
  function scheme_handler($xslt, $scheme, $rest) {
    echo "*";
    return '<?xml version="1.0" encoding="UTF-8"?><doc>fish</doc>';
  }

  $xslt = xslt_create();
  xslt_set_scheme_handlers($xslt, array("get_all" => "scheme_handler"));
  $args = array(
    "/_xml" => '<?xml version="1.0" encoding="UTF-8"?><test>TestValue</test>',
    "/_xsl" => '<?xml version="1.0" encoding="UTF-8"?>
                <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
                  <xsl:template match="test">
                    <xsl:value-of select="."/>: <xsl:value-of select="document('. "'test:/val'" .')/doc"/>
                  </xsl:template>
                </xsl:stylesheet>'
  );

  $data = xslt_process($xslt, "arg:/_xml", "arg:/_xsl", NULL, $args);

  // expect: TestValue: fish
  echo $data;

  xslt_free($xslt);
?>