+\subsection sec-order Order-only prerequisites
+
+If the static prerequisites of a rule contain a pipe symbol, prerequisites
+on its right do not cause the targets to become obsolete if they are newer
+(unless they are also dynamically registered as dependencies). They are
+meant to be used when the targets do not directly depend on them, but the
+computation of their dynamic dependencies does.
+
+@verbatim
+%.o : %.c | parser.h
+ gcc -MMD -MF $@.d -o $@ -c $<
+ remake -r < $@.d
+ rm $@.d
+
+parser.c parser.h: parser.y
+ yacc -d -o parser.c parser.y
+@endverbatim
+
+\subsection sec-special-var Special variables
+
+Variable <tt>.OPTIONS</tt> is handled specially. Its content enables some
+features of <b>remake</b> that are not enabled by default.
+
+- <tt>variable-propagation</tt>: When a variable is set in the prerequisite
+ part of a rule, it is propagated to the rules of all the targets this rule
+ depends on. This option also enables variables to be set on the command
+ line. Note that, as in <b>make</b>, this features introduces non-determinism:
+ the content of some variables will depend on the build order.
+