* HTML5, CSS, JavaScript and XML tutorials:
  - https://www.w3schools.com/
  - https://developer.mozilla.org/en-US/docs/Web
* XHTML5 (polyglot markup) usage:
  - https://wiki.whatwg.org/wiki/HTML_vs._XHTML
  - http://xmlplease.com/xhtml/xhtml5polyglot/
* Django API reference for templates:
  - https://docs.djangoproject.com/en/2.0/ref/templates/
* Unicode data support:
  - https://stackoverflow.com/questions/38363566/trouble-with-utf-8-characters-what-i-see-is-not-what-i-stored
* <meta> element usage:
  - https://moz.com/blog/seo-meta-tags
* Linkage to external style sheets or script files via the jsDelivr CDN:
  - https://www.jsdelivr.com/
* <label> element usage:
  - https://stackoverflow.com/questions/7636502/why-use-label
* Minimum length constraint for <input> elements:
  - https://stackoverflow.com/questions/10281962/is-there-a-minlength-validation-attribute-in-html5