Summary: called Art Page Borders If you are like me you ve gone 15 years without seeing or using this feature But it is there under the Format Borders and Shading menu on the Page Border tab The markup needed to define these borders is covered in section 2 18 4 ST Border Border Styles of the OOXML specification Here we see descriptions and images of 200 hundred or so Art
Image Dimensions: 540 x 505
Image originally found here.