Dan Goncharoff posts to ADS-L on this notice from New York City Parks and Recreation:
Beginning Monday, July 19, 2010, new rules take effect for vendors who sell art, photography, reading material, or sculpture in City parks. Vendors who sell these items are referred to as “Expressive Matter Vendors.” The new rules are available at http://www.nyc.gov/parks/rules.
The relevant point is the technical expression expressive matter (a mass nominal), designed to cover a category of creative productions that has no ordinary-language label, though it hangs together for people in the culture.
Considerable NYC coverage.
Meanwhile, the related mass nominal expressive material has some history as a legal term covering creative productions (including movies, computer files, published material of all kinds, and so on, as well as the material enumerated above) that might be subject to laws governing plagiarism, pornography, privacy, search and seizure, forfeiture, and the like.
Property subject to forfeiture may be seized by state, county or municipal law enforcement agencies upon process issued by any court having jurisdiction over the property upon a showing of probable cause; provided, however, that not more than one copy of each expressive material may be seized prior to a judicial determination, after a hearing at which all proper parties have an opportunity to be heard and present evidence, that the expressive material is obscene material or material which is harmful to minors and, in either case, subject to forfeiture under this division. (link)
That’s expressive material ‘item of expressive material’.