wiki.trwnh.com/content/tech/spec/activitypub/extensions/Emoji.md

Emoji

See for more: https://docs.joinmastodon.org/spec/activitypub/#emoji

A sub-type of Link that refers to a :custom_emoji:, typically used for replacing a plain-text substring with an inline image (by implementations that do not otherwise support arbitrary inline images).

Implementation details

Handling an Emoji is typically done by matching for the Emoji's name and replacing with an <img> element where src is the url of the Emoji's icon.

Note that this extension uses `icon` instead of `href`, but the same "search-and-replace" semantics apply, as with any microsyntax.

Consider the following Note:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    {
      "toot": "http://joinmastodon.org/ns#",
      "Emoji": "toot:Emoji"
    }
  ],

  "id": "https://example.com/@alice/hello-world",
  "type": "Note",
  "content": "<p>Hello world :kappa:</p>",
  "tag": [
    {
      "id": "https://example.com/emoji/123",
      "type": "Emoji",
      "name": ":kappa:",
      "icon": {
        "type": "Image",
        "mediaType": "image/png",
        "url": "https://example.com/files/kappa.png"
      }
    }
  ]
}

• We extract the natural-language properties of name, summary, and content. In this case, we have only content of Hello world :kappa:.
• We extract any elements from tag with a type of Emoji. In this case, we have only one, for :kappa:.
• We search for Emoji.name (:kappa:) within the identified content (Hello world :kappa:) and replace it with an inline image sourced from Emoji.icon.url (https://example.com/files/kappa.png), resulting in the final value for content being <p>Hello world <img src="https://example.com/files/kappa.png"/></p>.

Pseudocode might look something like this:

# Extract custom emojis from tag array
tags = Object.tag
Emojis = [tag for tag in tags where tag.type == "Emoji"]

for Emoji in Emojis:

  # replace :emoji: microsyntax with an inline image (within name)
  name = Object.name  # may need to extract `name` from `nameMap` instead
  name_matches = regex.match(substring = Emoji.name, text = name)
  for match in name_matches:
    search_and_replace(
      text = name,
      search = Emoji.name,
      replace = f'<img src={Emoji.icon.url}>'
      )

  # replace :emoji: microsyntax with an inline image (within summary)
  summary = Object.summary  # may need to extract `summary` from `summaryMap` instead
  summary_matches = regex.match(substring = Emoji.name, text = summary)
  for match in summary_matches:
    search_and_replace(
      text = summary,
      search = Emoji.name,
      replace = f'<img src={Emoji.icon.url}>'
      )

  # replace :emoji: microsyntax with an inline image (within content)
  content = Object.content  # may need to extract `content` from `contentMap` instead
  content_matches = regex.match(substring = Emoji.name, text = content)
  for match in content_matches:
    search_and_replace(
      text = content,
      search = Emoji.name,
      replace = f'<img src={Emoji.icon.url}>'
      )