Actions: Ensure well-formed and valid XML
diff --git a/.github/workflows/valid-xml.yml b/.github/workflows/valid-xml.yml
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+# __ __ _
+# ___\ \/ /_ __ __ _| |_
+# / _ \\ /| '_ \ / _` | __|
+# | __// \| |_) | (_| | |_
+# \___/_/\_\ .__/ \__,_|\__|
+# |_| XML parser
+#
+# Copyright (c) 2021 Sebastian Pipping <sebastian@pipping.org>
+# Licensed under the MIT license:
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to permit
+# persons to whom the Software is furnished to do so, subject to the
+# following conditions:
+#
+# The above copyright notice and this permission notice shall be included
+# in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+# NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+# DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+# OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+# USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+name: Ensure well-formed and valid XML
+
+on:
+ pull_request:
+ push:
+ schedule:
+ - cron: '0 2 * * 5' # Every Friday at 2am
+
+jobs:
+ checks:
+ name: Ensure well-formed and valid XML
+ runs-on: ubuntu-20.04
+ steps:
+ - uses: actions/checkout@v2.3.4
+
+ - name: Install build dependencies
+ run: |-
+ sudo apt-get install --yes --no-install-recommends -V \
+ docbook \
+ libxml2-utils \
+ w3c-sgml-lib
+
+ - name: Ensure well-formed and valid XML
+ run: |
+ set -x
+ xmllint --noout --valid expat/doc/reference.html
+ xmllint --noout --valid expat/doc/xmlwf.xml
