Creating a functional "blank line" or separator inside a custom column drop-down

[HappyCalibreUser]

If this should be located elsewhere maybe Library Management, I couldn't see how to locate it there. Sorry.

I finally found a way to do this and it works for me. Never saw mention of this when I searched before over 26 years now, if anyone is interested?
This is from Google's Chat.

Hope the blank character is visible in the post if not, Try google chat "Braille Blank Character"

To create a functional "blank line" or separator inside a Calibre custom column drop-down menu (specifically for an Enumerated Values column type), you cannot simply hit the spacebar or leave a field empty, as Calibre trims whitespace and rejects completely empty entries.
Instead, you can use specialized characters that look completely blank to Calibre's interface.

The Solution: Use the Braille Blank Character

The most effective trick is using the Braille Pattern Blank space (⠀). Unlike standard spaces or non-breaking spaces (which Calibre strips out), Calibre treats the Braille blank as a valid, unique character string while rendering it as completely invisible.

How to implement it:

1. Copy the invisible character inside the brackets below:
[⠀] (Only copy the blank space inside the brackets).
2. Go to your custom column settings in Preferences > Add your own columns.
3. In the Create a list of permitted values box, paste that character wherever you want a blank separator.
4. If you want multiple blank lines to act as dividers in different sections of your menu, you must make each one unique (otherwise Calibre merges them into one item). You can do this by pasting the character multiple times:
• First blank line: ⠀ (1 blank space)
• Second blank line: ⠀⠀ (2 blank spaces)
• Third blank line: ⠀⠀⠀ (3 blank spaces)

Alternative Option: Visible Dividers (which always looked clunky)

If you simply want to organize a long list of items, using a purely invisible line can sometimes cause accidental clicks. Many Calibre power users prefer using a clean, text-based visual separator instead:
• Paste a string of dashes: --------------------
• Use box-drawing lines: ────────────────────

If this is old news, or worthless, than please ignore it.

Hope everyone is having a good day.

[DNSB]

Or you can use Unicode U+2800 or HTML & #10240; to enter the character. An alternative is the Hangul Filler character (U+3164 or & #12644; ㅤ) which works equally well as a blank that is not characterized as a whitespace or format character. The space between the & and # is just to keep the character from being parsed.

The issue I've found with using such invisible characters is that your font or fallback fonts needs to be able to display the character otherwise you get the .notdef glyph which depend on the font and renderer as to what is displayed.

Though I suspect this should have been better placed in the calibre forum.

[DiapDealer]

Originally Posted by DNSB

Or you can use Unicode U+2800 or HTML & #10240; to enter the character. An alternative is the Hangul Filler character (U+3164 or & #12644; ㅤ) which works equally well as a blank that The space between the & and # is just to keep the character from being parsed.

You can use the noparse bbcode tag to prevent parsing entities. ⠀

Just leave the ampersand outside the noparse tag.