Documentation.

m4/check-package.m4

 dnl
 dnl Check for a library + header files
 dnl 
+dnl
+dnl Arguments:
+dnl
+dnl $1: symbolic name (fancy)
+dnl $2: library name (base name, lib$2[.so|.a]
+dnl $3: library path (-L$3)
+dnl $4: additional libraries needed (e.g. -lm -lGL)
+dnl $5: header name
+dnl $6: include path (-I$6
+dnl $7 \in \{optional, required\}, bail out if required, warning otherwise
+dnl
 AC_DEFUN(AC_CHECK_PKG,
 [AC_ARG_WITH($1-lib,
 [  --with-$1-lib=DIR   use $1 library below directory DIR (default: $3)],