Below is a left square brace, 10 spaces, and a right square brace, first in <blockquote>, then in <pre>
[ ]
[ ]
HTML source code:
<blockquote>[ ]</blockquote> <pre>[ ]</pre>
For just a few spaces, I use
& nbsp;& nbsp;& nbsp;
with the spaces removed after the ampersand.
Thanks for that tip, Cboldt! Captured it with the other note!