diff --git a/.drone.yml b/.drone.yml
new file mode 100644
index 0000000..09dee3b
--- /dev/null
+++ b/.drone.yml
@@ -0,0 +1,72 @@
+kind: pipeline
+name: Lint package
+
+volumes:
+- name: debian-package-cache
+  host:
+    path: /var/cache/debian-package-cache
+
+steps:
+- name: Emacs 26.3
+  image: flycheck/emacs-cask:26.3
+  pull: always
+  environment:
+    DEBIAN_FRONTEND: noninteractive
+    LANG: en_US.UTF-8
+  commands:
+  - rm /etc/apt/apt.conf.d/docker-clean
+  - alias apt-get='rm -f /var/cache/apt/archives/lock && apt-get'
+  - apt-get update -q
+  - apt-get install -qq language-pack-en git aspell-en
+  - ./makem.sh --verbose --sandbox --install-deps --install-linters lint
+  volumes:
+  - name: debian-package-cache
+    path: /var/cache/apt/archives
+
+- name: Emacs master-branch
+  image: flycheck/emacs-cask:master
+  pull: always
+  environment:
+    DEBIAN_FRONTEND: noninteractive
+    LANG: en_US.UTF-8
+  commands:
+  - rm /etc/apt/apt.conf.d/docker-clean
+  - alias apt-get='rm -f /var/cache/apt/archives/lock && apt-get'
+  - apt-get update -q
+  - apt-get install -qq language-pack-en git aspell-en
+  - emacs --version
+  - ./makem.sh --verbose --sandbox --install-deps --install-linters lint
+  volumes:
+  - name: debian-package-cache
+    path: /var/cache/apt/archives
+
+- name: Emacs 25.3
+  image: flycheck/emacs-cask:25.3
+  pull: always
+  environment:
+    DEBIAN_FRONTEND: noninteractive
+    LANG: C
+  commands:
+  - rm /etc/apt/apt.conf.d/docker-clean
+  - alias apt-get='rm -f /var/cache/apt/archives/lock && apt-get'
+  - apt-get update -q
+  - apt-get install -qq git
+  # Some package or its dependency requires Emacs 26.1,
+  # so we just check if it compiles.
+  - ./makem.sh --verbose --sandbox compile
+  volumes:
+  - name: debian-package-cache
+    path: /var/cache/apt/archives
+
+- name: notify
+  image: drillster/drone-email
+  pull: always
+  settings:
+    host: cryptoparty-celle.de
+    from: drone@tzend.de
+    username:
+      from_secret: email_username
+    password:
+      from_secret: email_password
+  when:
+    status: [ changed, failure ]
diff --git a/.gitignore b/.gitignore
index 9f27698..5983ed4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 /flycheck*.el*
 *~
+*.elc
diff --git a/makem.sh b/makem.sh
new file mode 100755
index 0000000..91c3000
--- /dev/null
+++ b/makem.sh
@@ -0,0 +1,1090 @@
+#!/usr/bin/env bash
+
+# * makem.sh --- Script to aid building and testing Emacs Lisp packages
+
+# https://github.com/alphapapa/makem.sh
+
+# * Commentary:
+
+# makem.sh is a script helps to build, lint, and test Emacs Lisp
+# packages.  It aims to make linting and testing as simple as possible
+# without requiring per-package configuration.
+
+# It works similarly to a Makefile in that "rules" are called to
+# perform actions such as byte-compiling, linting, testing, etc.
+
+# Source and test files are discovered automatically from the
+# project's Git repo, and package dependencies within them are parsed
+# automatically.
+
+# Output is simple: by default, there is no output unless errors
+# occur.  With increasing verbosity levels, more detail gives positive
+# feedback.  Output is colored by default to make reading easy.
+
+# The script can run Emacs with the developer's local Emacs
+# configuration, or with a clean, "sandbox" configuration that can be
+# optionally removed afterward.  This is especially helpful when
+# upstream dependencies may have released new versions that differ
+# from those installed in the developer's personal configuration.
+
+# * License:
+
+# 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 3 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/>.
+
+# * Functions
+
+function usage {
+    cat <<EOF
+$0 [OPTIONS] RULES...
+
+Linter- and test-specific rules will error when their linters or tests
+are not found.  With -vv, rules that run multiple rules will show a
+message for unavailable linters or tests.
+
+Rules:
+  all      Run all lints and tests.
+  compile  Byte-compile source files.
+
+  lint           Run all linters, ignoring unavailable ones.
+  lint-checkdoc  Run checkdoc.
+  lint-compile   Byte-compile source files with warnings as errors.
+  lint-declare   Run check-declare.
+  lint-elsa      Run Elsa (not included in "lint" rule).
+  lint-indent    Lint indentation.
+  lint-package   Run package-lint.
+  lint-regexps   Run relint.
+
+  test, tests           Run all tests, ignoring missing test types.
+  test-buttercup        Run Buttercup tests.
+  test-ert              Run ERT tests.
+  test-ert-interactive  Run ERT tests interactively.
+
+  batch        Run Emacs in batch mode, loading project source and test files
+               automatically, with remaining args (after "--") passed to Emacs.
+  interactive  Run Emacs interactively, loading project source and test files
+               automatically, with remaining args (after "--") passed to Emacs.
+
+Options:
+  -d, --debug    Print debug info.
+  -h, --help     I need somebody!
+  -v, --verbose  Increase verbosity, up to -vv.
+
+  --debug-load-path  Print load-path from inside Emacs.
+
+  -E, --emacs PATH  Run Emacs at PATH.
+
+  -e, --exclude FILE  Exclude FILE from linting and testing.
+  -f, --file FILE     Check FILE in addition to discovered files.
+
+  --no-color        Disable color output.
+  -C, --no-compile  Don't compile files automatically.
+
+Sandbox options:
+  -s[DIR], --sandbox[=DIR]  Run Emacs with an empty config in a sandbox DIR.
+                            If DIR does not exist, make it.  If DIR is not
+                            specified, use a temporary sandbox directory and
+                            delete it afterward, implying --install-deps and
+                            --install-linters.
+  --install-deps            Automatically install package dependencies.
+  --install-linters         Automatically install linters.
+  -i, --install PACKAGE     Install PACKAGE before running rules.
+
+  An Emacs version-specific subdirectory is automatically made inside
+  the sandbox, allowing testing with multiple Emacs versions.  When
+  specifying a sandbox directory, use options --install-deps and
+  --install-linters on first-run and omit them afterward to save time.
+
+Source files are automatically discovered from git, or may be
+specified with options.  Package dependencies are discovered from
+"Package-Requires" headers in source files, from -pkg.el files, and
+from a Cask file.
+EOF
+}
+
+# ** Elisp
+
+# These functions return a path to an elisp file which can be loaded
+# by Emacs on the command line with -l or --load.
+
+function elisp-buttercup-file {
+    # The function buttercup-run, which is called by buttercup-run-discover,
+    # signals an error if it can't find any Buttercup test suites.  We don't
+    # want that to be an error, so we define advice which ignores that error.
+    local file=$(mktemp)
+    cat >$file <<EOF
+(defun makem-buttercup-run (oldfun &rest r)
+  "Call buttercup-run only if \`buttercup-suites' is non-nil."
+  (when buttercup-suites
+    (apply oldfun r)))
+
+(advice-add #'buttercup-run :around #'makem-buttercup-run)
+EOF
+    echo $file
+}
+
+function elisp-checkdoc-file {
+    # Since checkdoc doesn't have a batch function that exits non-zero
+    # when errors are found, we make one.
+    local file=$(mktemp)
+
+    cat >$file <<EOF
+(defvar makem-checkdoc-errors-p nil)
+
+(defun makem-checkdoc-files-and-exit ()
+  "Run checkdoc-file on files remaining on command line, exiting non-zero if there are warnings."
+  (let* ((files (mapcar #'expand-file-name command-line-args-left))
+         (checkdoc-create-error-function
+          (lambda (text start end &optional unfixable)
+            (let ((msg (concat (checkdoc-buffer-label) ":"
+                               (int-to-string (count-lines (point-min) (or start (point-min))))
+                               ": " text)))
+              (message msg)
+              (setq makem-checkdoc-errors-p t)
+              (list text start end unfixable)))))
+    (mapcar #'checkdoc-file files)
+    (when makem-checkdoc-errors-p
+      (kill-emacs 1))))
+
+(setq checkdoc-spellcheck-documentation-flag t)
+(makem-checkdoc-files-and-exit)
+EOF
+    echo $file
+}
+
+function elisp-check-declare-file {
+    # Since check-declare doesn't have a batch function that exits
+    # non-zero when errors are found, we make one.
+    local file=$(mktemp)
+
+    cat >$file <<EOF
+(require 'check-declare)
+
+(defun makem-check-declare-files-and-exit ()
+  "Run check-declare-files on files remaining on command line, exiting non-zero if there are warnings."
+  (let* ((files (mapcar #'expand-file-name command-line-args-left))
+         (errors (apply #'check-declare-files files)))
+    (when errors
+      (with-current-buffer check-declare-warning-buffer
+        (print (buffer-string)))
+      (kill-emacs 1))))
+EOF
+    echo $file
+}
+
+function elisp-lint-indent-file {
+    # This function prints warnings for indentation errors and exits
+    # non-zero when errors are found.
+    local file=$(mktemp)
+
+    cat >"$file" <<EOF
+(require 'cl-lib)
+
+(defun makem-lint-indent-batch-and-exit ()
+  "Print warnings for files which are not indented properly, then exit.
+Exits non-zero if mis-indented lines are found.  Checks files in
+'command-line-args-left'."
+  (let ((errors-p))
+    (cl-labels ((lint-file (file)
+                           (find-file file)
+                           (let ((tick (buffer-modified-tick)))
+                             (let ((inhibit-message t))
+                               (indent-region (point-min) (point-max)))
+                             (when (/= tick (buffer-modified-tick))
+                               ;; Indentation changed: warn for each line.
+                               (dolist (line (undo-lines buffer-undo-list))
+                                 (message "%s:%s: Indentation mismatch" (buffer-name) line))
+                               (setf errors-p t))))
+                (undo-lines (undo-list)
+                            ;; Return list of lines changed in UNDO-LIST.
+                            (nreverse (cl-loop for elt in undo-list
+                                               when (and (consp elt)
+                                                         (numberp (car elt)))
+                                               collect (line-number-at-pos (car elt))))))
+      (mapc #'lint-file (mapcar #'expand-file-name command-line-args-left))
+      (when errors-p
+        (kill-emacs 1)))))
+EOF
+
+    echo "$file"
+}
+
+function elisp-package-initialize-file {
+    local file=$(mktemp)
+
+    cat >$file <<EOF
+(require 'package)
+(setq package-archives (list (cons "gnu" "https://elpa.gnu.org/packages/")
+                             (cons "melpa" "https://melpa.org/packages/")
+                             (cons "melpa-stable" "https://stable.melpa.org/packages/")))
+$elisp_org_package_archive
+(package-initialize)
+(setq load-prefer-newer t)
+EOF
+    echo $file
+}
+
+# ** Emacs
+
+function run_emacs {
+    # NOTE: The sandbox args need to come before the package
+    # initialization so Emacs will use the sandbox's packages.
+    local emacs_command=(
+        "${emacs_command[@]}"
+        -Q
+        "${args_debug[@]}"
+        "${args_sandbox[@]}"
+        -l $package_initialize_file
+        $arg_batch
+        "${args_load_paths[@]}"
+    )
+
+    # Show debug message with load-path from inside Emacs.
+    [[ $debug_load_path ]] \
+        && debug $("${emacs_command[@]}" \
+                       --batch \
+                       --eval "(message \"LOAD-PATH: %s\" load-path)" \
+                    2>&1)
+
+    # Set output file.
+    output_file=$(mktemp) || die "Unable to make output file."
+    paths_temp+=("$output_file")
+
+    # Run Emacs.
+    debug "run_emacs: ${emacs_command[@]} $@ &>\"$output_file\""
+    "${emacs_command[@]}" "$@" &>"$output_file"
+
+    # Check exit code and output.
+    exit=$?
+    [[ $exit != 0 ]] \
+        && debug "Emacs exited non-zero: $exit"
+
+    [[ $verbose -gt 1 || $exit != 0 ]] \
+        && cat $output_file
+
+    return $exit
+}
+
+# ** Compilation
+
+function batch-byte-compile {
+    debug "batch-byte-compile: ERROR-ON-WARN:$compile_error_on_warn"
+
+    [[ $compile_error_on_warn ]] && local error_on_warn=(--eval "(setq byte-compile-error-on-warn t)")
+
+    run_emacs \
+        "${error_on_warn[@]}" \
+        --funcall batch-byte-compile \
+        "$@"
+}
+
+# ** Files
+
+function dirs-project {
+    # Echo list of directories to be used in load path.
+    files-project-feature | dirnames
+    files-project-test | dirnames
+}
+
+function files-project-elisp {
+    # Echo list of Elisp files in project.
+    git ls-files 2>/dev/null \
+        | egrep "\.el$" \
+        | filter-files-exclude-default \
+        | filter-files-exclude-args
+}
+
+function files-project-feature {
+    # Echo list of Elisp files that are not tests and provide a feature.
+    files-project-elisp \
+        | egrep -v "$test_files_regexp" \
+        | filter-files-feature
+}
+
+function files-project-test {
+    # Echo list of Elisp test files.
+    files-project-elisp | egrep "$test_files_regexp"
+}
+
+function dirnames {
+    # Echo directory names for files on STDIN.
+    while read file
+    do
+        dirname "$file"
+    done
+}
+
+function filter-files-exclude-default {
+    # Filter out paths (STDIN) which should be excluded by default.
+    egrep -v "(/\.cask/|-autoloads.el|.dir-locals)"
+}
+
+function filter-files-exclude-args {
+    # Filter out paths (STDIN) which are excluded with --exclude.
+    if [[ ${files_exclude[@]} ]]
+    then
+        (
+            # We use a subshell to set IFS temporarily so we can send
+            # the list of files to grep -F.  This is ugly but more
+            # correct than replacing spaces with line breaks.  Note
+            # that, for some reason, using IFS="\n" or IFS='\n' doesn't
+            # work, and a literal line break seems to be required.
+            IFS="
+"
+            grep -Fv "${files_exclude[*]}"
+        )
+    else
+        cat
+    fi
+}
+
+function filter-files-feature {
+    # Read paths on STDIN and echo ones that (provide 'a-feature).
+    while read path
+    do
+        egrep "^\\(provide '" "$path" &>/dev/null \
+            && echo "$path"
+    done
+}
+
+function args-load-files {
+    # For file in $@, echo "--load $file".
+    for file in "$@"
+    do
+        printf -- '--load %q ' "$file"
+    done
+}
+
+function args-load-path {
+    # Echo load-path arguments.
+    for path in $(dirs-project | sort -u)
+    do
+        printf -- '-L %q ' "$path"
+    done
+}
+
+function test-files-p {
+    # Return 0 if $files_project_test is non-empty.
+    [[ "${files_project_test[@]}" ]]
+}
+
+function buttercup-tests-p {
+    # Return 0 if Buttercup tests are found.
+    test-files-p || die "No tests found."
+    debug "Checking for Buttercup tests..."
+
+    grep "(require 'buttercup)" "${files_project_test[@]}" &>/dev/null
+}
+
+function ert-tests-p {
+    # Return 0 if ERT tests are found.
+    test-files-p || die "No tests found."
+    debug "Checking for ERT tests..."
+
+    # We check for this rather than "(require 'ert)", because ERT may
+    # already be loaded in Emacs and might not be loaded with
+    # "require" in a test file.
+    grep "(ert-deftest" "${files_project_test[@]}" &>/dev/null
+}
+
+function dependencies {
+    # Echo list of package dependencies.
+
+    # Search package headers.
+    egrep -i '^;; Package-Requires: ' $(files-project-feature) $(files-project-test) \
+        | egrep -o '\([^([:space:]][^)]*\)' \
+        | egrep -o '^[^[:space:])]+' \
+        | sed -r 's/\(//g' \
+        | egrep -v '^emacs$'  # Ignore Emacs version requirement.
+
+    # Search Cask file.
+    if [[ -r Cask ]]
+    then
+        egrep '\(depends-on "[^"]+"' Cask \
+            | sed -r -e 's/\(depends-on "([^"]+)".*/\1/g'
+    fi
+
+    # Search -pkg.el file.
+    if [[ $(git ls-files ./*-pkg.el 2>/dev/null) ]]
+    then
+        sed -nr 's/.*\(([-[:alnum:]]+)[[:blank:]]+"[.[:digit:]]+"\).*/\1/p' $(git ls-files ./*-pkg.el 2>/dev/null)
+    fi
+}
+
+# ** Sandbox
+
+function sandbox {
+    verbose 2 "Initializing sandbox..."
+
+    # *** Sandbox arguments
+
+    # MAYBE: Optionally use branch-specific sandbox?
+
+    # Check or make user-emacs-directory.
+    if [[ $sandbox_dir ]]
+    then
+        # Directory given as argument: ensure it exists.
+        if ! [[ -d $sandbox_dir ]]
+        then
+            debug "Making sandbox directory: $sandbox_dir"
+            mkdir -p "$sandbox_dir" || die "Unable to make sandbox dir."
+        fi
+
+        # Add Emacs version-specific subdirectory, creating if necessary.
+        sandbox_dir="$sandbox_dir/$(emacs-version)"
+        if ! [[ -d $sandbox_dir ]]
+        then
+            mkdir "$sandbox_dir" || die "Unable to make sandbox subdir: $sandbox_dir"
+        fi
+    else
+        # Not given: make temp directory, and delete it on exit.
+        local sandbox_dir=$(mktemp -d) || die "Unable to make sandbox dir."
+        paths_temp+=("$sandbox_dir")
+    fi
+
+    # Make argument to load init file if it exists.
+    init_file="$sandbox_dir/init.el"
+
+    # Set sandbox args.  This is a global variable used by the run_emacs function.
+    args_sandbox=(
+        --title "makem.sh: $(basename $(pwd)) (sandbox: $sandbox_dir)"
+        --eval "(setq user-emacs-directory (file-truename \"$sandbox_dir\"))"
+        --eval "(setq user-init-file (file-truename \"$init_file\"))"
+    )
+
+    # Add package-install arguments for dependencies.
+    if [[ $install_deps ]]
+    then
+        local deps=($(dependencies))
+        debug "Installing dependencies: ${deps[@]}"
+
+        for package in "${deps[@]}"
+        do
+            args_sandbox_package_install+=(--eval "(package-install '$package)")
+        done
+    fi
+
+    # Add package-install arguments for linters.
+    if [[ $install_linters ]]
+    then
+        debug "Installing linters: package-lint relint"
+
+        args_sandbox_package_install+=(
+            --eval "(package-install 'elsa)"
+            --eval "(package-install 'package-lint)"
+            --eval "(package-install 'relint)")
+    fi
+
+    # *** Install packages into sandbox
+
+    if [[ ${args_sandbox_package_install[@]} ]]
+    then
+        # Initialize the sandbox (installs packages once rather than for every rule).
+        verbose 1 "Installing packages into sandbox..."
+
+        run_emacs \
+            --eval "(package-refresh-contents)" \
+            "${args_sandbox_package_install[@]}" \
+            && success "Packages installed." \
+                || die "Unable to initialize sandbox."
+    fi
+
+    verbose 2 "Sandbox initialized."
+}
+
+# ** Utility
+
+function cleanup {
+    # Remove temporary paths (${paths_temp[@]}).
+
+    for path in "${paths_temp[@]}"
+    do
+        if [[ $debug ]]
+        then
+            debug "Debugging enabled: not deleting temporary path: $path"
+        elif [[ -r $path ]]
+        then
+            rm -rf "$path"
+        else
+            debug "Temporary path doesn't exist, not deleting: $path"
+        fi
+    done
+}
+
+function echo-unset-p {
+    # Echo 0 if $1 is set, otherwise 1.  IOW, this returns the exit
+    # code of [[ $1 ]] as STDOUT.
+    [[ $1 ]]
+    echo $?
+}
+
+function ensure-package-available {
+    # If package $1 is available, return 0.  Otherwise, return 1, and
+    # if $2 is set, give error otherwise verbose.  Outputting messages
+    # here avoids repetition in callers.
+    local package=$1
+    local direct_p=$2
+
+    if ! run_emacs --load $package &>/dev/null
+    then
+        if [[ $direct_p ]]
+        then
+            error "$package not available."
+        else
+            verbose 2 "$package not available."
+        fi
+        return 1
+    fi
+}
+
+function ensure-tests-available {
+    # If tests of type $1 (like "ERT") are available, return 0.  Otherwise, if
+    # $2 is set, give an error and return 1; otherwise give verbose message.  $1
+    # should have a corresponding predicate command, like ert-tests-p for ERT.
+    local test_name=$1
+    local test_command="${test_name,,}-tests-p"  # Converts name to lowercase.
+    local direct_p=$2
+
+    if ! $test_command
+    then
+        if [[ $direct_p ]]
+        then
+            error "$test_name tests not found."
+        else
+            verbose 2 "$test_name tests not found."
+        fi
+        return 1
+    fi
+}
+
+function echo_color {
+    # This allows bold, italic, etc. without needing a function for
+    # each variation.
+    local color_code="COLOR_$1"
+    shift
+
+    if [[ $color ]]
+    then
+        echo -e "${!color_code}${@}${COLOR_off}"
+    else
+        echo "$@"
+    fi
+}
+function debug {
+    if [[ $debug ]]
+    then
+        function debug {
+            echo_color yellow "DEBUG ($(ts)): $@" >&2
+        }
+        debug "$@"
+    else
+        function debug {
+            true
+        }
+    fi
+}
+function error {
+    echo_color red "ERROR ($(ts)): $@" >&2
+    ((errors++))
+    return 1
+}
+function die {
+    [[ $@ ]] && error "$@"
+    exit $errors
+}
+function log {
+    echo "LOG ($(ts)): $@" >&2
+}
+function log_color {
+    local color_name=$1
+    shift
+    echo_color $color_name "LOG ($(ts)): $@" >&2
+}
+function success {
+    if [[ $verbose -ge 2 ]]
+    then
+        log_color green "$@" >&2
+    fi
+}
+function verbose {
+    # $1 is the verbosity level, rest are echoed when appropriate.
+    if [[ $verbose -ge $1 ]]
+    then
+        [[ $1 -eq 1 ]] && local color_name=blue
+        [[ $1 -ge 2 ]] && local color_name=cyan
+
+        shift
+        log_color $color_name "$@" >&2
+    fi
+}
+
+function ts {
+    date "+%Y-%m-%d %H:%M:%S"
+}
+
+function emacs-version {
+    # Echo Emacs version number.
+
+    # Don't use run_emacs function, which does more than we need.
+    "${emacs_command[@]}" -Q --batch --eval "(princ emacs-version)" \
+        || die "Unable to get Emacs version."
+}
+
+function rule-p {
+    # Return 0 if $1 is a rule.
+    [[ $1 =~ ^(lint-?|tests?)$ ]] \
+        || [[ $1 =~ ^(batch|interactive)$ ]] \
+        || [[ $(type -t "$2" 2>/dev/null) =~ function ]]
+}
+
+# * Rules
+
+# These functions are intended to be called as rules, like a Makefile.
+# Some rules test $1 to determine whether the rule is being called
+# directly or from a meta-rule; if directly, an error is given if the
+# rule can't be run, otherwise it's skipped.
+
+function all {
+    verbose 1 "Running all rules..."
+
+    lint
+    tests
+}
+
+function compile {
+    [[ $compile ]] || return 0
+    unset compile  # Only compile once.
+
+    verbose 1 "Compiling..."
+    debug "Byte-compile files: ${files_project_byte_compile[@]}"
+
+    batch-byte-compile "${files_project_byte_compile[@]}" \
+        && success "Compiling finished without errors." \
+            || error "Compilation failed."
+}
+
+function batch {
+    # Run Emacs in batch mode with ${args_batch_interactive[@]} and
+    # with project source and test files loaded.
+    verbose 1 "Executing Emacs with arguments: ${args_batch_interactive[@]}"
+
+    run_emacs \
+        $(args-load-files "${files_project_feature[@]}" "${files_project_test[@]}") \
+        "${args_batch_interactive[@]}"
+}
+
+function interactive {
+    # Run Emacs interactively.  Most useful with --sandbox and --install-deps.
+    verbose 1 "Running Emacs interactively..."
+    verbose 2 "Loading files:" "${files_project_feature[@]}" "${files_project_test[@]}"
+
+    unset arg_batch
+    run_emacs \
+        $(args-load-files "${files_project_feature[@]}" "${files_project_test[@]}") \
+        --eval "(load user-init-file)" \
+        "${args_batch_interactive[@]}"
+    arg_batch="--batch"
+}
+
+function lint {
+    verbose 1 "Linting..."
+
+    lint-checkdoc
+    lint-compile
+    lint-declare
+    lint-indent
+    lint-package
+    lint-regexps
+}
+
+function lint-checkdoc {
+    verbose 1 "Linting checkdoc..."
+
+    local checkdoc_file="$(elisp-checkdoc-file)"
+    paths_temp+=("$checkdoc_file")
+
+    run_emacs \
+        --load="$checkdoc_file" \
+        "${files_project_feature[@]}" \
+        && success "Linting checkdoc finished without errors." \
+            || error "Linting checkdoc failed."
+}
+
+function lint-compile {
+    verbose 1 "Linting compilation..."
+
+    compile_error_on_warn=true
+    batch-byte-compile "${files_project_byte_compile[@]}" \
+        && success "Linting compilation finished without errors." \
+            || error "Linting compilation failed."
+    unset compile_error_on_warn
+}
+
+function lint-declare {
+    verbose 1 "Linting declarations..."
+
+    local check_declare_file="$(elisp-check-declare-file)"
+    paths_temp+=("$check_declare_file")
+
+    run_emacs \
+        --load "$check_declare_file" \
+        -f makem-check-declare-files-and-exit \
+        "${files_project_feature[@]}" \
+        && success "Linting declarations finished without errors." \
+            || error "Linting declarations failed."
+}
+
+function lint-elsa {
+    verbose 1 "Linting with Elsa..."
+
+    # MAYBE: Install Elsa here rather than in sandbox init, to avoid installing
+    # it when not needed.  However, we should be careful to be clear about when
+    # packages are installed, because installing them does execute code.
+    run_emacs \
+        --load elsa \
+        -f elsa-run-files-and-exit \
+        "${files_project_feature[@]}" \
+        && success "Linting with Elsa finished without errors." \
+            || error "Linting with Elsa failed."
+}
+
+function lint-indent {
+    verbose 1 "Linting indentation..."
+
+    # We load project source files as well, because they may contain
+    # macros with (declare (indent)) rules which must be loaded to set
+    # indentation.
+
+    run_emacs \
+        --load "$(elisp-lint-indent-file)" \
+        $(args-load-files "${files_project_feature[@]}" "${files_project_test[@]}") \
+        --funcall makem-lint-indent-batch-and-exit \
+        "${files_project_feature[@]}" "${files_project_test[@]}" \
+        && success "Linting indentation finished without errors." \
+            || error "Linting indentation failed."
+}
+
+function lint-package {
+    ensure-package-available package-lint $1 || return $(echo-unset-p $1)
+
+    verbose 1 "Linting package..."
+
+    run_emacs \
+        --load package-lint \
+        --funcall package-lint-batch-and-exit \
+        "${files_project_feature[@]}" \
+        && success "Linting package finished without errors." \
+            || error "Linting package failed."
+}
+
+function lint-regexps {
+    ensure-package-available relint $1 || return $(echo-unset-p $1)
+
+    verbose 1 "Linting regexps..."
+
+    run_emacs \
+        --load relint \
+        --funcall relint-batch \
+        "${files_project_source[@]}" \
+        && success "Linting regexps finished without errors." \
+            || error "Linting regexps failed."
+}
+
+function tests {
+    verbose 1 "Running all tests..."
+
+    test-ert
+    test-buttercup
+}
+
+function test-ert-interactive {
+    verbose 1 "Running ERT tests interactively..."
+
+    unset arg_batch
+    run_emacs \
+        $(args-load-files "${files_project_test[@]}") \
+        --eval "(ert-run-tests-interactively t)"
+    arg_batch="--batch"
+}
+
+function test-buttercup {
+    ensure-tests-available Buttercup $1 || return $(echo-unset-p $1)
+    compile || die
+
+    verbose 1 "Running Buttercup tests..."
+
+    local buttercup_file="$(elisp-buttercup-file)"
+    paths_temp+=("$buttercup_file")
+
+    run_emacs \
+        $(args-load-files "${files_project_test[@]}") \
+        -f buttercup-run \
+        && success "Buttercup tests finished without errors." \
+            || error "Buttercup tests failed."
+}
+
+function test-ert {
+    ensure-tests-available ERT $1 || return $(echo-unset-p $1)
+    compile || die
+
+    verbose 1 "Running ERT tests..."
+    debug "Test files: ${files_project_test[@]}"
+
+    run_emacs \
+        $(args-load-files "${files_project_test[@]}") \
+        -f ert-run-tests-batch-and-exit \
+        && success "ERT tests finished without errors." \
+            || error "ERT tests failed."
+}
+
+# * Defaults
+
+test_files_regexp='^((tests?|t)/)|-tests?.el$|^test-'
+
+emacs_command=("emacs")
+errors=0
+verbose=0
+compile=true
+arg_batch="--batch"
+
+# MAYBE: Disable color if not outputting to a terminal.  (OTOH, the
+# colorized output is helpful in CI logs, and I don't know if,
+# e.g. GitHub Actions logging pretends to be a terminal.)
+color=true
+
+# TODO: Using the current directory (i.e. a package's repo root directory) in
+# load-path can cause weird errors in case of--you guessed it--stale .ELC files,
+# the zombie problem that just won't die.  It's incredible how many different ways
+# this problem presents itself.  In this latest example, an old .ELC file, for a
+# .EL file that had since been renamed, was present on my local system, which meant
+# that an example .EL file that hadn't been updated was able to "require" that .ELC
+# file's feature without error.  But on another system (in this case, trying to
+# setup CI using GitHub Actions), the old .ELC was not present, so the example .EL
+# file was not able to load the feature, which caused a byte-compilation error.
+
+# In this case, I will prevent such example files from being compiled.  But in
+# general, this can cause weird problems that are tedious to debug.  I guess
+# the best way to fix it would be to actually install the repo's code as a
+# package into the sandbox, but doing that would require additional tooling,
+# pulling in something like Quelpa or package-build--and if the default recipe
+# weren't being used, the actual recipe would have to be fetched off MELPA or
+# something, which seems like getting too smart for our own good.
+
+# TODO: Emit a warning if .ELC files that don't match any .EL files are detected.
+
+# ** Colors
+
+COLOR_off='\e[0m'
+COLOR_black='\e[0;30m'
+COLOR_red='\e[0;31m'
+COLOR_green='\e[0;32m'
+COLOR_yellow='\e[0;33m'
+COLOR_blue='\e[0;34m'
+COLOR_purple='\e[0;35m'
+COLOR_cyan='\e[0;36m'
+COLOR_white='\e[0;37m'
+
+# ** Package system args
+
+args_package_archives=(
+    --eval "(add-to-list 'package-archives '(\"gnu\" . \"https://elpa.gnu.org/packages/\") t)"
+    --eval "(add-to-list 'package-archives '(\"melpa\" . \"https://melpa.org/packages/\") t)"
+)
+
+args_org_package_archives=(
+    --eval "(add-to-list 'package-archives '(\"org\" . \"https://orgmode.org/elpa/\") t)"
+)
+
+args_package_init=(
+    --eval "(package-initialize)"
+)
+
+elisp_org_package_archive="(add-to-list 'package-archives '(\"org\" . \"https://orgmode.org/elpa/\") t)"
+
+# * Args
+
+args=$(getopt -n "$0" \
+              -o dhe:E:i:s::vf:CO \
+              -l exclude:,emacs:,install-deps,install-linters,debug,debug-load-path,help,install:,verbose,file:,no-color,no-compile,no-org-repo,sandbox:: \
+              -- "$@") \
+    || { usage; exit 1; }
+eval set -- "$args"
+
+while true
+do
+    case "$1" in
+        --install-deps)
+            install_deps=true
+            ;;
+        --install-linters)
+            install_linters=true
+            ;;
+        -d|--debug)
+            debug=true
+            verbose=2
+            args_debug=(--eval "(setq init-file-debug t)"
+                        --eval "(setq debug-on-error t)")
+            ;;
+        --debug-load-path)
+            debug_load_path=true
+            ;;
+        -h|--help)
+            usage
+            exit
+            ;;
+        -E|--emacs)
+            shift
+            emacs_command=($1)
+            ;;
+        -i|--install)
+            shift
+            args_sandbox_package_install+=(--eval "(package-install '$1)")
+            ;;
+        -s|--sandbox)
+            sandbox=true
+            shift
+            sandbox_dir="$1"
+
+            if ! [[ $sandbox_dir ]]
+            then
+                debug "No sandbox dir: installing dependencies."
+                install_deps=true
+            else
+                debug "Sandbox dir: $1"
+            fi
+            ;;
+        -v|--verbose)
+            ((verbose++))
+            ;;
+        -e|--exclude)
+            shift
+            debug "Excluding file: $1"
+            files_exclude+=("$1")
+            ;;
+        -f|--file)
+            shift
+            args_files+=("$1")
+            ;;
+        -O|--no-org-repo)
+            unset elisp_org_package_archive
+            ;;
+        --no-color)
+            unset color
+            ;;
+        -C|--no-compile)
+            unset compile
+            ;;
+        --)
+            # Remaining args (required; do not remove)
+            shift
+            rest=("$@")
+            break
+            ;;
+    esac
+
+    shift
+done
+
+debug "ARGS: $args"
+debug "Remaining args: ${rest[@]}"
+
+# Set package elisp (which depends on --no-org-repo arg).
+package_initialize_file="$(elisp-package-initialize-file)"
+paths_temp+=("$package_initialize_file")
+
+# * Main
+
+trap cleanup EXIT INT TERM
+
+# Discover project files.
+files_project_feature=($(files-project-feature))
+files_project_test=($(files-project-test))
+files_project_byte_compile=("${files_project_feature[@]}" "${files_project_test[@]}")
+
+if [[ ${args_files[@]} ]]
+then
+    # Add specified files.
+    files_project_feature+=("${args_files[@]}")
+    files_project_byte_compile+=("${args_files[@]}")
+fi
+
+debug "EXCLUDING FILES: ${files_exclude[@]}"
+debug "FEATURE FILES: ${files_project_feature[@]}"
+debug "TEST FILES: ${files_project_test[@]}"
+debug "BYTE-COMPILE FILES: ${files_project_byte_compile[@]}"
+
+if ! [[ ${files_project_feature[@]} ]]
+then
+    error "No files specified and not in a git repo."
+    exit 1
+fi
+
+# Set load path.
+args_load_paths=($(args-load-path))
+debug "LOAD PATH ARGS: ${args_load_paths[@]}"
+
+# If rules include linters and sandbox-dir is unspecified, install
+# linters automatically.
+if [[ $sandbox && ! $sandbox_dir ]] && [[ "${rest[@]}" =~ lint ]]
+then
+    debug "Installing linters automatically."
+    install_linters=true
+fi
+
+# Initialize sandbox.
+[[ $sandbox ]] && sandbox
+
+# Run rules.
+for rule in "${rest[@]}"
+do
+    if [[ $batch || $interactive ]]
+    then
+        debug "Adding batch/interactive argument: $rule"
+        args_batch_interactive+=("$rule")
+
+    elif [[ $rule = batch ]]
+    then
+        # Remaining arguments are passed to Emacs.
+        batch=true
+    elif [[ $rule = interactive ]]
+    then
+        # Remaining arguments are passed to Emacs.
+        interactive=true
+
+    elif type -t "$rule" 2>/dev/null | grep function &>/dev/null
+    then
+        # Pass called-directly as $1 to indicate that the rule is
+        # being called directly rather than from a meta-rule.
+        $rule called-directly
+    elif [[ $rule = test ]]
+    then
+        # Allow the "tests" rule to be called as "test".  Since "test"
+        # is a shell builtin, this workaround is required.
+        tests
+    else
+        error "Invalid rule: $rule"
+    fi
+done
+
+# Batch/interactive rules.
+[[ $batch ]] && batch
+[[ $interactive ]] && interactive
+
+if [[ $errors -gt 0 ]]
+then
+    log_color red "Finished with $errors errors."
+else
+    success "Finished without errors."
+fi
+
+exit $errors