diff --git a/documents/Makefile b/documents/Makefile
index 2384eb9..d60c795 100644
--- a/documents/Makefile
+++ b/documents/Makefile
@@ -1,24 +1,34 @@
 DOCUMENT_NAMES=asymmetrie chaosradio copyleft intro mailserviceanbieter mozilla outlook pgp_vs_gnupg senselab thunderbird thunderbirdnutzung warumverschluesselung wiefunktionierts winpt
 
+# our self written documents
 LYX_FILES := $(foreach dir,$(DOCUMENT_NAMES),$(dir)/$(dir).lyx)
+# the tex output of lyx
 TEX_FILES := $(patsubst %.lyx,%.tex,$(LYX_FILES))
+# output files of lyx that are already processed by mod_html_files.py
 HTML_FILES := $(patsubst %.lyx,%.html,$(LYX_FILES))
+# headers, navigation and footers are added (according to online/offline target)
 TARGET_FILES := $(foreach dir,$(DOCUMENT_NAMES),_output/$(dir).html)
+# header, navigation and footer files
 ASC_FILES := $(wildcard *.asc)
+# target: online or offline (will be overriden for online target automatically)
 LINE_STATUS = offline
 
+
+# output parameters for latex2html
 LATEX2HTMLPREFIX := -no_auto_link -split 0 -no_navigation -no_subdir -dir _output -info 0 -style cryptocd.css -local_icons -address 0
 
 
-.PHONY : clean online offline clean-targets install
+# virtual targets that have different names than the produced files - they will alway be executed,
+# if another target depends on them (they do not look for timestamps)
+.PHONY : clean online offline clean-targets install all
 
 # default target (offline)
 all: $(HTML_FILES)
 
+
+# copy the created files to the destination directory (usually outside of this directory tree)
 install: $(TARGET_FILES)
-    ifndef CCD_BUILD_DIR
-      $(error "CCD_BUILD_DIR must be defined!")
-    endif
+	@[ -z "$(CCD_BUILD_DIR)" ] && echo "CCD_BUILD_DIR must be defined! (this should be done by the parent Makefile)" >&2 && false
 	@if [ ! -e "$(CCD_BUILD_DIR)" ] ; \
 		then	echo "CCD_BUILD_DIR ($(CCD_BUILD_DIR)) does not exist!" ; \
 			exit 1 ; \
@@ -29,10 +39,13 @@ install: $(TARGET_FILES)
 clean-targets:
 	-rm $(TARGET_FILES) 2>/dev/null
 
+
 online:	 LINE_STATUS=online
 offline: LINE_STATUS=offline
 online offline: clean-targets $(TARGET_FILES)
 
+
+# add headers, navigation and footers
 $(TARGET_FILES): $(HTML_FILES) $(ASC_FILES)
 	cat nav.$(LINE_STATUS).asc $(notdir $(basename $@))/$(notdir $@) >$@