I like this idea, and considering the usage of a OpenGraph-like pattern, I'd like to propose extra metadata for custom embeds in fluxer, something like this:
<!-- This would allow Fluxer to know if a link should prompt a confirmation to join a community when clicked --><metaname="fluxer:invite-code" content="eDfgY33P"><!-- These tags would define the custom embed for a site, if missing, standard metadata is used as fallback --><metaname="fluxer:embed-title" content="Example title"><metaname="fluxer:embed-url" content="https://example.com"><metaname="fluxer:embed-image" content="https://example.com/image.png"><metaname="fluxer:embed-color" content="#AABBCC">
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Comment by @Fer2G