Flagging content that is "free" for text mining - Crossref

"The Crossref API can be used for locating the full text of published articles and preprints for the purpose of text mining. Crossref members who have have subscription-access content and who want to make some of their content available for text mining need to take the following steps. The Crossref schema supports the NISO Access and License Indicators ALI section, and, normally, the free_to_read functionality of ALI would be the recommended mechanism for indicating that content is available for free (e.g. “gratis”, not “open”). However, the ALI free_to_read element is not currently exposed through our REST API filters. But we have defined a workaround that allows members to both register the ALI free_to_read element and an equivalent assertion that will work with the REST API and which will allow researchers to locate content that has been flagged as “free.”..."