RE
no Tabs for Normal View and HTML Source - scratch that
I did not notice that the All-In-One layout puts the Custom Controls in a Scrollable Panel, so you have to scroll the entire panel to see the 2 tabs - that's OK now that I know - but maybe the 2 tabs should be at the top of the Long Text control, rather than at the bottom.
I actually noticed the Scrollable Panel in the Compact Layout, today was the first time I selected it.
So leaving aside the Book Link issue - I have 2 change requests
1 - Show the External Name of Long Text Columns on the Book Details Panel
2 - Provide a field on the Insert Link dialogue for the Display Label ie
And the resultant HTML would be
<a href="URL">Label</a>
BR