An Occasion for the Arts, the annual festival celebrating all things artistic, opens Friday at 6 p.m. in Merchants Square, Williamsburg, and continues through Sunday on Duke of Gloucester Street. Festival hours are 10 a.m.-5 p.m. Saturday and Sunday. Admission is free. The Friday concert will feature Pressing Strings, an Annapolis-based indie-folk and soul band. The show will include nearly 150 artists in the Main Street zone, 34 area artists at The Front Porch, the Avant Garden with a K-12 student art exhibit, and a Virginia hip-hop history on foot....