category of municipal bond distinguished from public purpose bond in the tax reform act of 1986 because 10% or more of the bond's benefit goes to private activities or 5% of the proceeds (or $5 million if less) are used for loans to parties other than governmental units. Private purpose obligations, which are also called private activity bonds or nonessential function bonds, are taxable unless their use is specifically exempted. Even tax-exempt permitted private activity bonds, if issued after August 7, 1986, are tax preference items, except those issued for 501(c)(3) organizations (hospitals, colleges, universities). Private purpose bonds specifically prohibited from tax-exemption effective August 15, 1986, include those for sports, trade, and convention facilities and large-issue (over $1 million) Industrial Development Bonds. Permitted issues, except those for 501(c)(3) organizations, airports, docks, wharves, and government-owned solid-waste disposal facilities, are subject to volume caps.