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Going through (some) previous non-lab observable examples, this attribute is not used.
Observables PG Meeting 2016-08-01
Rob Hausam: the two are synonyms, without difference in meaning, hence, why should there be different attribute names? The reasons are purely technical. Proposal to make two (sub-)attributes Procedure component and Observable component. Cf. Procedure site and Finding site.
Recommendation from Observables PG
New attribute "Observable component" and rename existing "Component" attribute to "Procedure component".