The complete project configuration file is shown here, presenting options for additional extensions, multiple projects, etc.
# XMake PROJECT CONFIGURATION FILE
# This file is for common XMake options; read before
# reading any makefiles
# Additional options may be configured in
# $XMAKE_PROJECT_DIR/XMakefile

# This project configuration file "XMake.conf", must
# reside at the top level project directory.
# XMAKE_PROJECT_CONF_FILE is automatically set to this
# file, if found in the current path.
# XMAKE_PROJECT_DIR is set to the directory containing
# this file BEFORE this file is read

export XMAKE_SHELL_CMD=/usr/local/bin/bash
# or, if you install make as non-root user, use something
# like:
# export XMAKE_BUILD_CMD=$HOME/bin/make
export XMAKE_BUILD_CMD=/usr/local/bin/make

# auto-detect XMExtension source files with:
# export XMAKE_AUTODETECT_SOURCE_FILES=1
# otherwise:
# Each directory may include a makefile,
# "XM_sources.mkh", defining local source files
# The file must set the variable XM_sources:
# XM_sources+= /abs/path/to/file1 /abs/path/to/file2 ...
export XMAKE_AUTODETECT_SOURCE_FILES=1

# private directory for temporary files; shared by
# XMExtensions makefiles
# this directory is automatically created by XMake
export \
XMAKE_TMP_DIR=${XMAKE_PROJECT_DIR}/${XMAKE_TMP_DIR_NAME}

# XMAKE_IGNORE_DIRS_RE
# Extended Regular Expression specifying subdirectories
# to ignore;
# I.e., excluded from project; no rules to make targets
# in ignored directories
# A standard prefix for directories to be ignored is
# already defined:
# XMAKE_IGNORE_DIR_NAME_PREFIX=XMakeIgnore
# Any directories named "XMakeIgnore*" will be ignored
XMAKE_IGNORE_DIRS_RE='(/'$XMAKE_EXTENSIONS_DIR_NAME'$)|('$XMAKE_TMP_DIR'$)|(/'$XMAKE_IGNORE_DIR_NAME_PREFIX')|(/CVS$)|(/RCS$)|(/SCCS$)'
export XMAKE_IGNORE_DIRS_RE

# XMAKE_FINAL_TARGETS_PATTERN
# Include directories where static library files and
# headers are kept, for example.
# This pattern is used in $(filter ...) command
# Targets matching the pattern will be:
#	removed from $(XM_externalTargets)
#		+ avoids trying to recursively make files which are
# outside any XMake project
#	added to $(XM_finalTargets)
#		+ creates an empty rule for these targets
XMAKE_FINAL_TARGETS_PATTERN='/usr/lib/% /usr/include/%'
export XMAKE_FINAL_TARGETS_PATTERN

# XMAKE_RECURSION
# if XMAKE_RECURSION=1, targets outside this project
# scope are made, recursively
# external XMake targets are automatically built prior to
# any other targets
# This value will be overridden by command line options:
# -x, -X
XMAKE_RECURSION=1

# XMAKE_BUILD_CMD_OPTIONS are automatically used when
# invoking XMAKE_BUILD_CMD
export XMAKE_BUILD_CMD_OPTIONS=-r

# XMAKE_MAKEFILES_SEARCH is used to find the initial
# makefile unless -f option overrides
# To emulate GNU make (if you have an existing project
# that uses Gnu makefiles):
# use the following setting:
# XMAKE_MAKEFILES_SEARCH="GNUMakefile makefile Makefile"
# Normally ${XMAKE_MASTER_HEADER} should come init :
export XMAKE_MAKEFILES_SEARCH="${XMAKE_MASTER_HEADER} \
GNUMakefile makefile Makefile"

# Using $XMAKE_DOCUMENT_ROOT you can create links that
# will work in the web server environment.
# set $XMAKE_DOCUMENT_ROOT equal to the same value as
# $DOCUMENT_ROOT that applies to the project and reference
# it from your .phpc file, for example:
#<?php echo '<a
# href="$XMAKE_DOCUMENT_ROOT'.'relative/path/to/file.html">file.html</a>';
# ?>
export XMAKE_DOCUMENT_ROOT=/usr/local/apache/htdocs/

# XMAKE_EXTENSIONS includes the names of all XMake
# Extensions that handle source files
# SETTINGS FROM THE ENVIRONMENT OVERRIDE
# This value will be overridden by command line options:
# -E
# All XMExtensions are disabled if XMAKE_EXTENSIONS is
# empty
# The format can list extensions, by name, or:
# XMAKE_EXTENSIONS='all' # enables all extensions
# XMAKE_EXTENSIONS='none' # disables all extensions
# a subset of XMExtensions prefixed by '-' are excluded
# EXAMPLE: include all except t2h, c
#: ${XMAKE_EXTENSIONS='all -t2h -c'}; export
# XMAKE_EXTENSIONS
# EXAMPLE: include only phpc, xdir
#: ${XMAKE_EXTENSIONS='phpc xdir'}; export
# XMAKE_EXTENSIONS
#: ${XMAKE_EXTENSIONS='c xdir'}; export XMAKE_EXTENSIONS
: ${XMAKE_EXTENSIONS='phpc t2h'}; export XMAKE_EXTENSIONS

######################################################
# XMExtension Options
# Options for all XMExtensions were copied here during
# project creation
# If XMExtensions are subsequently installed, copy the
# global config options
# into this file
######################################################
######################################################
# c XMExtension
# global config file:
#
# /usr/local/apache/htdocs/common/xmake/config/XMExtensions/c.conf
######################################################
export XMAKE_XME_C=/usr/bin/cc
######################################################
######################################################
# phpc XMExtension
# global config file:
#
# /usr/local/apache/htdocs/common/xmake/config/XMExtensions/phpc.conf
######################################################
# XMAKE_XME_PHPC is the path to command line PHP (SAPI
# CLI)
export XMAKE_XME_PHPC=/usr/local/bin/php
# XMAKE_EXT_PHPC_PHP_INI optionally specifies the php.ini
# file;
# if not specified, the default is used:
# /usr/local/lib/php.ini
export XMAKE_EXT_PHPC_PHP_INI=
# XMAKE_XME_PHPC_FATAL_ERROR_MASK controls which error
# codes are fatal
# E_WARNING|E_USER_ERROR|E_USER_WARNING=2|256|512=770
export XMAKE_XME_PHPC_FATAL_ERROR_MASK=770
# XMAKE_XME_PHPC_FATAL_ERROR_MASK controls fatal errors
# for targets:
# phpc.lint, php.lint
# XMAKE_XME_PHPC_LINT_FATAL_ERROR_MASK=0;
# don't exit, display as many errors as possible on
# /dev/stderr
export XMAKE_XME_PHPC_LINT_FATAL_ERROR_MASK=0
######################################################
######################################################
# t2h XMExtension
# global config file:
#
# /usr/local/apache/htdocs/common/xmake/config/XMExtensions/t2h.conf
######################################################
######################################################
######################################################
# xdir XMExtension
# global config file:
#
# /usr/local/apache/htdocs/common/xmake/config/XMExtensions/xdir.conf
######################################################
export XMAKE_XME_XDIR=/bin/cat
######################################################