custom node isn't being exported to collection metadata

[tintou]

Per the collection specification, the custom node isn't visible, would it make sense to add it there (we are using it in elementary AppCenter to enhance our store).

[ximion]

What do you mean with "isn't visible"? Does libappstream not read it when it's present (it should), or is the custom entry not present in the source XML? In the latter case, the issue is with your metadata generator, which, in case it's appstream-generator, will need a whitelist of allowed custom keys that it should put into the generated XML or YAML.
See AllowedCustomKeys in https://github.com/ximion/appstream-generator/blob/master/docs/asgen-config.md#toplevel-fields for reference.

[tintou]

Unfortunately, for flatpak that's still libappstream-glib, and it produces a metadata entry instead of custom (per https://github.com/hughsie/appstream-glib/blob/e98c97fcd4e0ffa17b00f842c9bad462bf7c3afb/libappstream-glib/as-app.c#L4834 ) but that should be fixed by at least increasing the version in hughsie/appstream-glib#407
This bug is more toward the specification that doesn't seem to cover this field, even in the optional case.

[ximion]

What do you expect the specification to say about it? Looks like you kind of already found the source of your issue, with a solution for it.
The custom tag is, by definition, optional.

[ximion]

Closing, as bug is stale.