Support fragment indexing

[pavelzw]

Version of Marp Tool

@marp-team/marp-cli v2.3.0 (w/ @marp-team/marp-core v3.4.2)

Operating System

macOS

Environment

• OS version: macOS Ventura 13.1
• Node.js version (Marpit / Marp Core/ Marp CLI): 19.4.0

How to reproduce

test.md

---
marp: true
---

<div data-marpit-fragments="3">
  <div data-marpit-fragment="2">
    two
  </div>
  <div data-marpit-fragment="1">
    one
  </div>
  <div data-marpit-fragment="3">
    three
  </div>
</div>

marp --html -o test.html test.md

Expected behavior

two <- gets revealed second
one <- gets revealed first
three <- gets revealed third

Actual behavior

two <- gets revealed first
one <- gets revealed second
three <- gets revealed third

Additional information

No response

[pavelzw]

Related to maro-team/marpit#264.

[yhatt]

As described at marp-team/marpit#264, Marp only respects DOM order. (Actually indexes assigned to data-marpit-fragment attribute are for another presentation tool made from Marpit framework)

We think it will make confusion that the fragments order is different from visible order, so hints by index number are ignored in Marp. To implement this, we require clear benefit and strong incentive.

[pavelzw]

In my opinion, it is a bit confusing to support index numbers but then have them ignored by marp-cli. I think that the hybrid solution you mentioned here sounds like a good tradeoff.

[yhatt]

Close for cleaning up Marp CLI issue tracker. Continue at marp-team/marpit#264 to avoid fragmented discussions at duplicated issues.