+#
+# SYNOPSIS
+#
+# AE_FEATURE(FEATURE-NAME, FEATURE-DESCRIPTION,
+# ACTION-IF-GIVEN?, ACTION-IF-NOT-GIVEN?,
+# ACTION-IF-ENABLED?, ACTION-IF-NOT-ENABLED?)
+#
+# DESCRIPTION
+#
+# AE_FEATURE is a simple wrapper for AC_ARG_ENABLE.
+#
+# FEATURE-NAME should consist only of alphanumeric characters, dashes,
+# plus signs, and dots.
+#
+# FEATURE-DESCRIPTION will be formatted with AS_HELP_STRING.
+#
+# If the user gave configure the option --enable-FEATURE or --disable-FEATURE,
+# run shell commands ACTION-IF-GIVEN. If neither option was given, run shell
+# commands ACTION-IF-NOT-GIVEN. The name feature indicates an optional
+#
+# If the feature is enabled, run shell commands ACTION-IF-ENABLED, if it is
+# disabled, run shell commands ACTION-IF-NOT-ENABLED.
+#
+# A FEATURE has 3 different states, enabled, disabled and undefined. The first
+# two are self explanatory, the third state means it's disabled by default
+# and it was not explicitly enabled or disabled by the user or by the
+# AE_FEATURE_ENABLE and AE_FEATURE_DISABLE macros.
+#
+# A feature is disabled by default, in order to change this behaviour use the
+# AE_FEATURE_DEFAULT_ENABLE and AE_FEATURE_DEFAULT_DISABLE
+# macros.
+#
+# A simple example:
+#
+# AE_FEATURE_DEFAULT_ENABLE
+# AE_FEATURE(feature_xxxxx, [turns on/off XXXXX support])
+#
+# ...
+#
+# AE_FEATURE_DEFAULT_DISABLE
+# AE_FEATURE(feature_yyyyy, [turns on/off YYYYY support])
+# AM_CONDITIONAL(YYYYY, AE_IS_FEATURE_ENABLED([feature_yyyyy]))
+#
+# AE_FEATURE_DEFAULT_ENABLE
+# AE_FEATURE(...)
+#
+# ...
+#
+# Use AE_FEATURE_ENABLE or AE_FEATURE_DISABLE in order to
+# enable or disable a specific feature.
+#
+# Another simple example:
+#
+# AS_IF([some_test_here],[AE_FEATURE_ENABLE(feature_xxxxx)],[])
+#
+# AE_FEATURE(feature_xxxxx, [turns on/off XXXXX support],
+# HAVE_XXXXX, [Define if you want XXXXX support])
+# AE_FEATURE(feature_yyyyy, [turns on/off YYYYY support],
+# HAVE_YYYYY, [Define if you want YYYYY support])
+#
+# ...
+#
+# NOTE: AE_FEATURE_ENABLE/DISABLE() must be placed first of the relative
+# AE_FEATURE() macro if you want the the proper ACTION-IF-ENABLED and
+# ACTION-IF-NOT-ENABLED to run.
+#
+# LICENSE
+#
+# Copyright (c) 2020 Michael Jeanson <mjeanson@efficios.com>
+# Copyright (c) 2008 Francesco Salvestrini <salvestrini@users.sourceforge.net>
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by the
+# Free Software Foundation; either version 2 of the License, or (at your
+# option) any later version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+# Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program. If not, see <https://www.gnu.org/licenses/>.
+#
+# As a special exception, the respective Autoconf Macro's copyright owner
+# gives unlimited permission to copy, distribute and modify the configure
+# scripts that are the output of Autoconf when processing the Macro. You
+# need not follow the terms of the GNU General Public License when using
+# or distributing such scripts, even though portions of the text of the
+# Macro appear in them. The GNU General Public License (GPL) does govern
+# all other use of the material that constitutes the Autoconf Macro.
+#
+# This special exception to the GPL applies to versions of the Autoconf
+# Macro released by the Autoconf Archive. When you make and distribute a
+# modified version of the Autoconf Macro, you may extend this special
+# exception to the GPL to apply to your modified version as well.
+
+#serial 1
+
+
+# AE_FEATURE_DEFAULT_ENABLE: The next feature defined with AE_FEATURE will
+# default to enable.
+AC_DEFUN([AE_FEATURE_DEFAULT_ENABLE], [
+ m4_define([ae_feature_default_arg], [yes])
+ m4_define([ae_feature_default_switch], [disable])
+])
+
+
+# AE_FEATURE_DEFAULT_DISABLE: The next feature defined with AE_FEATURE will
+# default to disable.
+#
+AC_DEFUN([AE_FEATURE_DEFAULT_DISABLE], [
+ m4_define([ae_feature_default_arg], [no])
+ m4_define([ae_feature_default_switch], [enable])
+])
+
+
+# AE_FEATURE_ENABLE(FEATURE-NAME): Enable the FEATURE, this will override the
+# user's choice if it was made.
+#
+AC_DEFUN([AE_FEATURE_ENABLE],[ dnl
+ enable_[]patsubst([$1], -, _)[]=yes
+])
+
+
+# AE_FEATURE_DISABLE(FEATURE-NAME): Disable the FEATURE, this will override the
+# user's choice if it was made.
+#
+AC_DEFUN([AE_FEATURE_DISABLE],[ dnl
+ enable_[]patsubst([$1], -, _)[]=no
+])
+
+
+# AE_IF_FEATURE_ENABLED(FEATURE-NAME, ACTION-IF-ENABLED, ACTION-IF-NOT-ENABLED?):
+# Run shell code ACTION-IF-ENABLED if the FEATURE is enabled, otherwise run
+# shell code ACTION-IF-NOT-ENABLED.
+#
+AC_DEFUN([AE_IF_FEATURE_ENABLED],[ dnl
+m4_pushdef([FEATURE], patsubst([$1], -, _))dnl
+
+ AS_IF([test "$enable_[]FEATURE[]" = yes],[ dnl
+ $2
+ ],[: dnl
+ $3
+ ])
+])
+
+
+# AE_IF_FEATURE_NOT_ENABLED(FEATURE-NAME, ACTION-IF-NOT-ENABLED,
+# ACTION-IF-NOT-NOT-ENABLED?):
+# Run shell code ACTION-IF-NOT-ENABLED if the FEATURE is not explicitly
+# enabled, otherwise run shell code ACTION-IF-NOT-NOT-DISABLED.
+#
+# The distinction with AE_IF_FEATURE_DISABLED is that this will also
+# match a feature that is undefined.
+#
+# A feature is undefined when it's disabled by default and was not explicitly
+# enabled or disabled by the user or by AE_FEATURE_ENABLE/DISABLE.
+#
+AC_DEFUN([AE_IF_FEATURE_NOT_ENABLED],[ dnl
+m4_pushdef([FEATURE], patsubst([$1], -, _))dnl
+
+ AS_IF([test "$enable_[]FEATURE[]" != yes],[ dnl
+ $2
+ ],[: dnl
+ $3
+ ])
+])
+
+
+# AE_IF_FEATURE_DISABLED(FEATURE-NAME, ACTION-IF-DISABLED, ACTION-IF-NOT-DISABLED?):
+# Run shell code ACTION-IF-DISABLED if the FEATURE is disabled, otherwise run
+# shell code ACTION-IF-NOT-DISABLED.
+#
+AC_DEFUN([AE_IF_FEATURE_DISABLED],[ dnl
+m4_pushdef([FEATURE], patsubst([$1], -, _))dnl
+
+ AS_IF([test "$enable_[]FEATURE[]" = no],[ dnl
+ $2
+ ],[: dnl
+ $3
+ ])
+])
+
+
+# AE_IF_FEATURE_UNDEF(FEATURE-NAME, ACTION-IF-UNDEF, ACTION-IF-NOT-UNDEF?):
+# Run shell code ACTION-IF-UNDEF if the FEATURE is undefined, otherwise run
+# shell code ACTION-IF-NOT-UNDEF.
+#
+# A feature is undefined when it's disabled by default and was not explicitly
+# enabled or disabled by the user or by AE_FEATURE_ENABLE/DISABLE.
+#
+AC_DEFUN([AE_IF_FEATURE_UNDEF],[ dnl
+m4_pushdef([FEATURE], patsubst([$1], -, _))dnl
+
+ AS_IF([test "x$enable_[]FEATURE[]" = x],[ dnl
+ $2
+ ],[: dnl
+ $3
+ ])
+])
+
+
+# AE_IS_FEATURE_ENABLED(FEATURE-NAME): outputs a shell condition (suitable
+# for use in a shell if statement) that will return true if the FEATURE is
+# enabled.
+#
+AC_DEFUN([AE_IS_FEATURE_ENABLED],[dnl
+m4_pushdef([FEATURE], patsubst([$1], -, _))dnl
+ test "x$enable_[]FEATURE[]" = xyes dnl
+])
+
+
+dnl Disabled by default, unless already overriden
+m4_ifndef([ae_feature_default_arg],[AE_FEATURE_DEFAULT_DISABLE])
+
+
+# AE_FEATURE(FEATURE-NAME, FEATURE-DESCRIPTION,
+# ACTION-IF-GIVEN?, ACTION-IF-NOT-GIVEN?,
+# ACTION-IF-ENABLED?, ACTION-IF-NOT-ENABLED?):
+#
+#
+AC_DEFUN([AE_FEATURE],[ dnl
+m4_pushdef([FEATURE], patsubst([$1], -, _))dnl
+
+dnl If the option wasn't specified and the default is enabled, set enable_FEATURE to yes
+AS_IF([test "x$enable_[]FEATURE[]" = x && test "ae_feature_default_arg" = yes],[ dnl
+ enable_[]FEATURE[]="ae_feature_default_arg"
+])
+
+AC_ARG_ENABLE([$1],
+ AS_HELP_STRING([--ae_feature_default_switch-$1],dnl
+ [$2 [default=ae_feature_default_arg]]),[
+case "${enableval}" in
+ yes)
+ enable_[]FEATURE[]=yes
+ ;;
+ no)
+ enable_[]FEATURE[]=no
+ ;;
+ *)
+ AC_MSG_ERROR([bad value ${enableval} for feature --$1])
+ ;;
+esac
+
+$3
+],[: dnl
+$4
+])
+
+AS_IF([test "$enable_[]FEATURE[]" = yes],[: dnl
+ $5
+],[: dnl
+ $6
+])
+
+m4_popdef([FEATURE])dnl
+])