It seems to be dependent both on the browser reading it and on the software that processes submitted HTML.
<tt> should just change the font but not the formatting - things should get justified just as usual for HTML text. You don't want ABC justified. Mudcat inserts <br> linebreaks when within <tt> tags, which is non-standard but in this instance helpful.
X:1
T:Scholion of Seikilos
M:6/8
L:1/8
Q:3/8=44
K:AMix
Ae2 e3 |(cde) d3 |c2d e(dc)|cA2 (BG2) |
Ace d(cd)| cA2 (BG2)|AcB dec |AA2 A(FE)|]
<pre> should mean that what you enter gets reproduced with exactly the layout you typed, but on Mudcat it doesn't - each line gets prefixed with a space (which buggers up ABC). This is probably fixable at Mudcat's end. I can't imagine any reason why it might be a good idea, ever.
X:1
T:Scholion of Seikilos
M:6/8
L:1/8
Q:3/8=44
K:AMix
Ae2 e3 |(cde) d3 |c2d e(dc)|cA2 (BG2) |
Ace d(cd)| cA2 (BG2)|AcB dec |AA2 A(FE)|]
<code> sets Mudcat off on an orgy of converting spaces to codes. I can't imagine why.
X:1
T:Scholion of Seikilos
M:6/8
L:1/8
Q:3/8=44
K:AMix
Ae2 e3 |(cde) d3 |c2d e(dc)|cA2 (BG2) |
Ace d(cd)| cA2 (BG2)|AcB dec |AA2 A(FE)|]
So, for ABC the way I do it, <tt> looks like the best bet. (Look at the source for this page to see exactly what Mudcat's message-processing front end does).
I was led down this road by another board that doesn't support HTML in posts directly, but instead uses BBCode. In that environment, [code] ... [/code] works well (nothing else does), so it seemed worth trying the HTML equivalent here.