+# (callable) Get the modified time of the provided file.
+#
+# Only the date·time information available via `ls -l´ is supported; that is, only minute precision for files newer than six months, and only day precision for files which are older.
+# This is, unfortunately, the best that can be done in pure Posix as of now.
+#
+# There is an easier implementation which provides the full date·time by archiving an empty file and then reading it back out of the archive :—
+#
+# $(shell LC_TIME=POSIX TZ=UTC0 $(TOUCH) -m -r $(callquote,$1) $(BUILDDIR)/.mtime && $(PAX) -w -x ustar $(BUILDDIR)/.mtime | $(PAX) -v -o 'listopt=%(mtime=%Y-%m-%dT%H:%M:%SZ)T')
+#
+# However, it depends on the `listopt´ option in `pax´, which (despite being specified in Posix) no implementations actually support.
+#
+# ☡ This variable creates a subshell every time it is computed.
+override modtime = $(shell { $(DATE) -u '+%Y-%m'; LC_TIME=POSIX TZ=UTC0 ls -q -A -l $(call quote,$1) | $(SED) 's/\([^ ]* \{1,\}\)\{5\}\(\([^ ]* \{1,\}\)\{3\}\).*/\2/;s/ \([0123456789]\) / 0\1 /;s/Jan/01/;s/Feb/02/;s/Mar/03/;s/Apr/04/;s/May/05/;s/Jun/06/;s/Jul/07/;s/Aug/08/;s/Sep/09/;s/Oct/10/;s/Nov/11/;s/Dec/12/;s/\([0123456789]\{2\}\) *\([0123456789]\{2\}\) *\([0123456789]\{4\}\)/\3-\1-\2T00:00:00Z/;s/\([0123456789]\{2\}\) *\([0123456789]\{2\}\) *\([0123456789:]\{5\}\)/XXXX-\1-\2T\3:00Z/'; } | $(TR) -d ' ' | $(AWK) -F '-' 'NR==1{year=$$1;month=$$2}$$1=="XXXX"&&$$2<=month{print year"-"$$2"-"$$3}$$1=="XXXX"&&$$2>month{print year-1"-"$$2"-"$$3}NR>1&&$$1!="XXXX"')
+
+# ─ ¶ Recipe Variable Definitions ─────────────────────────────────────
+
+# (callable) Check to see if the given directory exists and create it if not.
+override ensuredirectory = if $(TEST) ! -d $(call quote,$1); then $(MKDIR) -p $(call quote,$1); fi
+
+# Quote standard input in such a way that piping it to xargs will result in it being processed as a single argument.
+#
+# If standard input ends in a newline, it is stripped; all other newlines are preserved.
+override xargsquote = $(SED) $(call quote,s/'/'"'"'/g;s/^/'/;s/$$/'/;$$!s/$$/\\/)
+
+# Quote standard input in such a way that piping it to xargs will result in each line being processed as a single argument.
+override xargsmultiquote = $(SED) $(call quote,s/'/'"'"'/g;s/^/'/;s/$$/'/)
+
+# (callable) Test if the provided xpath expression matches the provided document.
+override xpath = $(XMLLINT) --xpath $(call quote,$1) $(call quote,$2) > /dev/null 2> /dev/null
+
+# (callable) Extract the value of the text nodes in the provided X·M·L document and print them to `stdout´.
+override extracttext = $(PRINTF) '%s' '<transform xmlns="http://www.w3.org/1999/XSL/Transform" version="1.0"><output method="text" encoding="UTF-8"/></transform>' | $(XSLTPROC) --nonet --novalid - $(call quote,$1)
+
+# (callable) Process the provided transformation result and output the result to the provided location, given the provided relative path.
+override processresultto = if $(call xpath,/*[local-name()="raw-text" and namespace-uri()="urn:fdc:ladys.computer:20231231:Shu1She4"],$1); then $(call extracttext,$1) > $(call quote,$2); elif $(call xpath,/*[local-name()="base64-binary" and namespace-uri()="urn:fdc:ladys.computer:20231231:Shu1She4"],$1); then { $(PRINTF) '%s\n' 'begin-base64 644 -'; $(call extracttext,$1) | $(TR) -d '\t\n\f\r '; $(PRINTF) '\n%s\n' '===='; } | $(UUDECODE) -o /dev/stdout > $(call quote,$2); elif $(call xpath,/*[local-name()="archive" and namespace-uri()="urn:fdc:ladys.computer:20231231:Shu1She4"],$1); then $(MAKE) -f $(call quote,$(abspath $(THISDIR)/GNUmakefile)) $(call quote,$2) NAME=$(call quote,$3) SRC=$(call quote,$1) BUILDDIR=$(call quote,$(BUILDDIR)/archive/$3) DESTDIR=$(call quote,$(patsubst %/,%,$(dir $2))) MODE='urn:fdc:ladys.computer:20231231:Shu1She4:mode:archive'; else $(XMLLINT) --nsclean $(call quote,$1) > $(call quote,$2); fi
+
+# ━ § BEGIN DEFAULT MAKE·FILE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+ifeq ($(MODE),urn:fdc:ladys.computer:20231231:Shu1She4:mode:default)
+
+# ─ ¶ Non‐Recipe Variable Definitions ─────────────────────────────────
+
+# (callable) Test to see if the prerequisites provided by the second argument matches the value in the file corresponding to the first argument in `$(BUILDDIR)/lastprereqs´.
+# If not, save the new value and then add FORCE.
+# Return them regardless.
+#
+# Calling this variable is useful when a given target should be updated whenever its list of prerequisites changes in addition to whenever there is a change to one of its prerequisites.
+#
+# ☡ This variable creates at least one subshell every time it is computed.
+override diffprereqs = $(if $(subst $(shell $(CAT) $(call quote,$(BUILDDIR)/lastprereqs/$1) 2> /dev/null || true),,$2),$2 FORCE$(and $(shell $(call ensuredirectory,$(BUILDDIR)/lastprereqs) && $(PRINTF) '%s\n' $(call quote,$2) > $(BUILDDIR)/lastprereqs/$1),),$2)
+
+# (callable) Escape special characters for use in sed regular expressions.
+override sedesc = $(subst /,[/],$(subst $$,\$$,$(subst *,\*,$(subst .,\.,$(subst [,\[,$(subst ^,\^,$(subst \,\\,$1)))))))
+
+# The command to use for percent‐decoding.
+override perdeccmd := $(SED) 's/|/%7C/g;s/[\]/%5C/g;s/%[0123456789ABCDEFabcdef]\{2\}/|&|/g' | $(TR) '|' '\n' | $(SED) '/^%[0123456789ABCDEFabcdef]\{2\}$$/!s/%/|%25|/' | $(TR) '|' '\n' | $(AWK) '$$0!~/%/{printf "%s",$$0}/%/{d="0123456789ABCDEF";v=substr(toupper($$0),2,2);printf "\\%04o",(index(d,substr(v,1,1))-1)*16+index(d,substr(v,2,1))-1}' | $(xargsquote) | $(XARGS) -E '' $(PRINTF) '%b'