The example Makefile provided has the line:
pdf_proc = java org.apache.fop.apps.Fop -fo $(fo_flags)
$(in) -pdf $(out)
but if you define fo_flags to be something, Fop
complains. The above line should be:
pdf_proc = java org.apache.fop.apps.Fop $(fo_flags) -fo
$(in) -pdf $(out)