How to use vim to write a aligned plain text (txt) file as the vim help files?

vim help files are in plain text format. They'are under /vim/vim80/doc.Lots of <Tab> characters are used to align the contents.

Interestingly, I can't find a good way to write such <Tab> aligned texts by vim. Every plugin use space to align words. Some bring this issue up on these project homes, and no solution is provided.

I'm curious how the vim developers write the help documents?

Plugins
-----------------------------------------------------------
vim-easy-align: Align to Nearest Tabstop #58 https://git.io/fAdXc
tabular: https://git.io/fAdXW

Excerpted from vim's help
-----------------------------------------------------------
Development of Vim. *development*

This text is important for those who want to be involved in further developing
Vim.

1. Design goals |design-goals|
2. Coding style |coding-style|
3. Design decisions |design-decisions|
4. Assumptions |design-assumptions|

--
--
You received this message from the "vim_use" maillist.
Do not top-post! Type your reply below the text you are replying to.
For more information, visit http://www.vim.org/maillist.php

---
You received this message because you are subscribed to the Google Groups "vim_use" group.
To unsubscribe from this group and stop receiving emails from it, send an email to vim_use+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.