+#
+# -c uses PDF and the poppler library via pdftocairo for generating
+# bitmaps, simulating the output for Evince and other previewers
+# using poppler. pdftocairo may be contained in the poppler-utils
+# package.
+#
+# -r can be used for specifying a rendering resolution. This
+# defaults to 101 for poppler and 300 for Ghostscript from PDF.
+#
+# -g uses Ghostscript for rendering a bitmap version from the PDF,
+# simulating the output from printing PDF files on a GNU system, so
+# use a resolution appropriate for print. Antialiasing is not enabled.
+#
+# -d changes the Ghostscript device used for creating PNG files
+# (usually png16m for direct PNG creation and pngmono for printer simulation)
+#
+# if any filenames follow, those are the tests to run. In absence
+# of any filenames, the contents of input/regression are used.