+ifndef FONTDIR
+$(info FONTDIR is not defined, defauling to AONROOTDIR/common/fonts/)
+FONTDIR := $(AONROOTDIR)/common/fonts/
+endif
+
+# Sanity checks before going further
+ifndef SERIES
+$(error WARNING: Book series is not defined, please define variable 'SERIES')
+endif
+ifndef BLANG
+$(error WARNING: Book language is not defined, please define variable 'BLANG')
+endif
+ifndef BASENAME
+$(error WARNING: Book basic name is not defined, please define variable 'BASENAME')
+endif
+
+