diff --git a/Pmodules/modbuild.in b/Pmodules/modbuild.in
index ca8a785..4aeb388 100755
--- a/Pmodules/modbuild.in
+++ b/Pmodules/modbuild.in
@@ -188,11 +188,13 @@ declare --	opt_debug='no'
 declare --      opt_yaml='yes'
 declare --	opt_variant=''
 declare --	opt_clean_install='no'
+declare --	opt_parent_prefix=''
 
 declare --	BUILD_SCRIPT=''
 declare --      yaml_config_file=''
 declare -a      legacy_config_files=()
 declare --	module_name=''
+declare --	module_type='module'
 declare --	echo=':'
 
 parse_args() {
@@ -327,6 +329,16 @@ parse_args() {
 				shift
 			fi
 			;;
+		--parent-prefix | --parent-prefix=* )
+			if [[ $1 == *=* ]]; then
+				opt_parent_prefix=( "${1#--*=}" )
+			else
+				opt_parent_prefix=( "$2" )
+				shift
+			fi
+			module_type='sub_package'
+			pbuild.set_prefix "${opt_parent_prefix}"
+			;;
                 -- | '' )
                         :
                         ;;
@@ -335,9 +347,8 @@ parse_args() {
 			;;
 		* )
 			local -- arg="$1"
-			local -- tmpvar=$(std::get_abspath "${arg}")
-			if [[ -r ${tmpvar} ]]; then
-				BUILD_SCRIPT="${tmpvar}"
+			if [[ -r ${arg} ]]; then
+				BUILD_SCRIPT="$(std::get_abspath "${arg}")"
 				BUILDBLOCK_DIR=$(dirname "${BUILD_SCRIPT}")
 			elif [[ "${arg}" == */* ]]; then
 				module_name="${arg%/*}"
@@ -362,7 +373,7 @@ parse_args() {
 	opt_system="${opt_system:-$(std::get_os_release)}"
 
 	# set config file
-	if [[ ${opt_yaml,,} != 'yes' ]]; then
+	if [[ ${opt_yaml,,} == 'no' ]]; then
 		# look for legacy config files
 		if [[ -n ${opt_config_file} ]]; then
 			legacy_config_files=( "${opt_config_file}" )
@@ -550,6 +561,16 @@ build_modules_yaml(){
 	shift 2
         local -a with_modules=( $* )
 
+
+	if [[ "${opt_check_mode}" == 'yes' ]]; then
+		local -- yamllint
+		if ! which yamllint > /dev/null 2>&1; then
+			eval $( "${MODULECMD}" bash load yamllint/1.28.0 )
+		fi
+		which yamllint > /dev/null 2>&1 || \
+			std::die 3 "yamllint not found"
+		yamllint "${yaml_config_file}"
+	fi
 	local -- file_fmt=$(get_yaml_file_fmt "${yaml_config_file}")
 	
 	local -- yaml_mod_config=''
@@ -567,17 +588,45 @@ build_modules_yaml(){
 	esac
 }
 
-# these variables must be export for envsubst(1)
-declare -x P=''
-declare -x V=''
-declare -x V_PKG=''
-declare -x V_MAJOR=''		# first number in version string
-declare -x V_MINOR=''		# second number in version string (or empty)
-declare -x V_PATCHLVL=''	# third number in version string (or empty)
-declare -x V_RELEASE=''		# module release (or empty)
+#......................................................................
+#
+# Initialise environment modules.
+#
+# Arguments:
+#	none
+#
+init_module_environment(){
+	eval $( "${MODULECMD}" bash use unstable )
+	eval $( "${MODULECMD}" bash use deprecated )
+	eval $( "${MODULECMD}" bash purge )
 
-declare -A SHASUMS=()
-declare -a MODULE_DOCFILES=()
+	# :FIXME: this is a hack!!!
+	# shouldn't this be set in the build-script?
+	if [[ -e "${PMODULES_HOME%%/Tools*}/Libraries" ]]; then
+		eval $( "${MODULECMD}" bash use Libraries )
+	fi
+	if [[ -e "${PMODULES_HOME%%/Tools*}/System" ]]; then
+		eval $( "${MODULECMD}" bash use System )
+	fi
+	unset	C_INCLUDE_PATH
+	unset	CPLUS_INCLUDE_PATH
+	unset	CPP_INCLUDE_PATH
+	unset	LIBRARY_PATH
+	unset	LD_LIBRARY_PATH
+	unset	DYLD_LIBRARY_PATH
+
+	unset	CFLAGS
+	unset	CPPFLAGS
+	unset	CXXFLAGS
+	unset	LIBS
+	unset	LDFLAGS
+
+	unset	CC
+	unset	CXX
+	unset	FC
+	unset	F77
+	unset	F90
+}
 
 parse_version() {
 	local v="$1"
@@ -623,11 +672,24 @@ parse_version() {
 	fi
 	VERSIONS+=( ${V_MAJOR} )
 }
+# these variables must be export for envsubst(1)
+declare -x P=''
+declare -x V=''
+declare -x V_PKG=''
+declare -x V_MAJOR=''		# first number in version string
+declare -x V_MINOR=''		# second number in version string (or empty)
+declare -x V_PATCHLVL=''	# third number in version string (or empty)
+declare -x V_RELEASE=''		# module release (or empty)
+
+declare -A SHASUMS=()
+declare -a MODULE_DOCFILES=()
+
 
 declare -A Yaml_valid_keys_for_module=(
-	['defaults']=1			# !!map
-	['shasums']=1			# !!map
-	['versions']=1			# !!int
+	['defaults']=1
+	['shasums']=1
+	['type']=1
+	['versions']=1
 )
 
 declare -A Yaml_default_config=(
@@ -649,6 +711,7 @@ declare -A Yaml_default_config=(
 	["script"]='build'		# !!str
 	["suffix"]=''			# !!str
 	["systems"]=''			# !!seq of strings
+	["sub_packages"]=''		# !!map
 	["urls"]=''			# !!map
 	["variant"]=''			# !!str
 )
@@ -724,8 +787,8 @@ build_modules_yaml_v1(){
 		local -- yaml_input="$1"
 		local -n cfg="$2"	# ref. to return configuration
 		local -n dfl="$3"       # ref. to defaults
-		local -- key
-		local -- value
+		local -- key=''
+		local -- value=''
 
 		for key in "${!dfl[@]}"; do
 			cfg[${key}]="${dfl[${key}]}"
@@ -739,7 +802,6 @@ build_modules_yaml_v1(){
 		keys=( $( ${yq} -e ".|keys().[]" <<<"${yaml_input}" 2>/dev/null )) || \
 			std::die 3 "Oops: retrieving keys from:\n${yaml_input}"
 		debug "config keys: ${keys[@]}"
-		local -- type;
 		for key in "${keys[@]}"; do
 			[[ -v dfl[${key,,}] ]] || \
 				std::die 3 "%s -- %s\n%s" \
@@ -802,7 +864,7 @@ build_modules_yaml_v1(){
 							;;
 					esac
 					;;
-				urls )
+				urls | sub_packages )
 					get_value "${yaml_input}" value "${key}" '!!seq'
 					cfg[${key,,}]="${value}"
 					;;
@@ -1151,7 +1213,6 @@ build_modules_yaml_v1(){
 		l=$( ${yq} -Ne e '.|length'  <<<"${yaml}" 2>/dev/null) || \
 			std::die 3 "error parsing YAML configuration"
 		local -i i=0
-		local -- fname=''
 		local -- url_yaml=''
 		for ((i=0; i<l; i++)); do
 			url_yaml=$(${yq} -Ne e ".[$i]" <<<"${yaml}" 2>/dev/null) || \
@@ -1159,6 +1220,8 @@ build_modules_yaml_v1(){
 			local url=''
 			local fname=''
 			local strip_dirs=''
+			local key=''
+			local value=''
 			while read key value; do
 				key=${key:0:-1}
 				case "${key}" in
@@ -1199,6 +1262,57 @@ build_modules_yaml_v1(){
 		pbuild.add_patch_files "${args[@]}"
 	}
 
+	build_sub_packages(){
+		local -- yaml="$1"
+		local -i l=0
+		l=$( ${yq} -Ne e '.|length'  <<<"${yaml}" 2>/dev/null) || \
+			std::die 3 "error parsing YAML configuration"
+		local -i i=0
+		local -- fname=''
+		local -- pkgs_yaml=''
+		for ((i=0; i<l; i++)); do
+			pkgs_yaml=$(${yq} -Ne e ".[$i]" <<<"${yaml}" 2>/dev/null) || \
+				std::die 3 "error parsing YAML configuration"
+			local -- pkg_name=''
+			local -- pkg_version=''
+			local -a pkg_build_args=()
+			local -a keys=()
+			keys=( $( ${yq} -e ".|keys().[]" <<<"${pkgs_yaml}" 2>/dev/null )) || \
+				std::die 3 "Oops: retrieving keys from:\n${yaml_input}"
+			local -- key=''
+			for key in "${keys[@]}"; do
+				case ${key,,} in
+					'name' )
+						get_value "${pkgs_yaml}" pkg_name "${key}" '!!str'
+						;;
+					'version' )
+						get_value "${pkgs_yaml}" pkg_version "${key}" '!!str'
+						;;
+					'build_args' )
+						local -- value=''
+						get_seq "${pkgs_yaml}" value "${key}"
+						readarray -t pkg_build_args <<< "${value}"
+						;;
+					* )
+						std::die 3 "%s -- %s\n%s" \
+							 "Invalid key in configuration" \
+							 "${key}" "${yaml_input}"
+						;;
+				esac
+			done
+			[[ "${opt_verbose}" == 'yes' ]] && \
+				pkg_build_args+=( '--verbose' )
+			[[ "${opt_debug}" == 'yes' ]] && \
+				pkg_build_args+=( '--debug' )
+			[[ "${opt_force_rebuild}" == 'yes' ]] && \
+				pkg_build_args+=( '-f' )
+			pkg_build_args+=( "--parent-prefix=${PREFIX}" )
+			"$BUILDBLOCK_DIR/build-${pkg_name}" \
+				"${pkg_name}/${pkg_version}" \
+				"${pkg_build_args[@]}"
+		done
+	}
+
 	build_modules_variant(){
 		local -- module_name="$1"
 		local -- module_version="$2"
@@ -1287,6 +1401,7 @@ build_modules_yaml_v1(){
 			"${module_version}" \
 			module_config \
 			"${runtime_deps[@]}" "${build_requires[@]}"
+		build_sub_packages "${module_config['sub_packages']}"
 	}
 
 	expand_version_key(){
@@ -1332,8 +1447,23 @@ build_modules_yaml_v1(){
 			SHASUMS[${key//:}]="${value}"
 		done <<<"${yaml_input}"
 	fi
-	
-	
+	if [[ -v used_keys['type'] ]]; then
+		local -- value=''
+		get_value "${yaml_mod_config}" value 'type' '!!str'
+		case "${value,,}" in
+			'module' )
+				[[ "${module_type}" == 'sub_package' ]] && \
+					std::die 3 "Module type is 'module' but was called as 'sub_package'!"
+				;;
+			'sub_package' )
+				[[ "${module_type}" == 'module' ]] && \
+					std::die 3 "Module type is 'sub_package' but was called as 'module'!"
+				;;
+			* )
+				std::die 3 "Invalid module type -- '${value}'!"
+				;;
+		esac
+	fi
 	get_matching_version_keys version_keys "${version}" <<<"${yaml_mod_config}"
 	for version_key in "${version_keys[@]}"; do
 		local yaml_vk_config=$(get_yaml_vk_config "${version_key}" <<<"${yaml_mod_config}")