The font for this test case has an AAT Extended Glyph Metamorphosis Table with a single Contextual Glyph Substitution Subtable. Its finite-state machine contains a single state with the following transitions:

The input string for this test is ABCDE. If your rendering system correctly implements Apple Advanced Typography, it should do the following when processing the transition for D: first, it should replace the marked glyph B by a circled form. Second, it should reset the marked glyph index to D. Therefore, only the B letter should be encircled in the rendered result. If the D is encircled, your implementation should be fixed to reset the marked glyph index after performing the replacement.