It:html5

Tidying HTML5 code

This uses the veritable program TIDY, now supporting HTML5. The code can be found at http://www.html-tidy.org It operates from the command line, and can be incorporated into text editors using scripts.

Use via BBedit

This MacOS X program goes back to the early days of HTML, and now supports Tidy as follows

1. Install the latest version of Tidy for OS X from http://binaries.html-tidy.org (in fact, Tidy comes pre-installed on OS X, so only do this if you want the latest version)
2. Create a script containing the lines

#!/bin/sh
/usr/bin/tidy -f /dev/null -config ~/Library/Application\ Support/tidyconfig.txt
   exit 0

1. Save it to a file tidy_up.sh and save this file into /Users/USERNAME/Library/Application\ Support/BBEdit/Text Filters/
2. Using File:Tidyconfig.txt place this into ~/Library/Application\ Support/ (You can edit the settings as you wish)
3. Invoke Tidy from BBedit via Menu: Text/Apply text filer/tidy_up

Adding special characters such as chemical arrows

A good collection of various types of arrow is seen at https://www.w3schools.com/charsets/ref_utf_arrows.asp