java com.icl.saxon.StyleSheet -o build/index.html signate-docs.xml libs/html-cust.xsl
Error at xsl:value-of on line 238 of file:/usr/share/xml/docbook/stylesheet/nwalsh/current/html/graphics.xsl:
  Exception in extension function java.lang.InternalError: Can't connect to X11 window server using ':0.0' as the value of the DISPLAY variable.
Transformation failed: Run-time errors were reported
make: *** [index] Error 2