ConceptScheme URI is limited to http(s) schema

[xloggr]

Currently only http(s) URLs are allowed as ConceptScheme URI values.

In fact, URIs can have other schemas. Moreover, a URN is a valid subtype of a URI.
For example, specifying the following valid URIs as ConceptScheme values results in empty SKOS output for otherwise valid spreadsheets:

• ftp://example.com/rdf.
• tag:example.com,2000:/rdf

Note: I only tried the online version of the SKOS Play!

[tfrancart]

I confirm the issue