Animation-friendly export

[nixonyh]

Description

Making the export more animation-friendly, e.g. by exposing some way to generate groups with well-known identifiers in SVG export, which external tools can pick up.

Use Case

Ideally, users can label Typst object (box or block for now):

#box(fill: white, stroke: black)[= Typst] <title>

Then during a Svg export, Typst will add the name of these labels as an identifier in the Svg:

<g id="title" x="10" y="10">
</g>

[nixonyh]

We might want a consensus on how we want to set ids for repetitions.

In some cases like enums, lists, or blocks that are "breakable", we generate a Fragment for them. A Fragment consists of multiple Frames which ultimately leads to multiple svg groups. This means that if we tag these elements with a Label e.g.

#block() [
  ...
] <block-label>

We might end up with multiple svg groups having the same id. How would you guys want to approach this problem? The goal here is to prevent id repetition, it's part of the spec of svg.

Here are my suggestions:

1. Ignore the repetition, repeat it anyways, it's used for animations, who cares! (Not recommended tho)
2. Append a new hash for each of the id after the label name regardless of repetition (this means that intentionally repeated Labels in typst would be ignored since each of them has their own hash appended to the Label itself: (label#58sn4g, label#783khs)
3. Treat repeatable Label content with care. When items are repeated, append a number behind it: label#0, label#1, label#2, etc. If there are no repetitions, use the original label without appending any numbers behind it. (My personal preference)