The font for this test case supports the “joining style” of Ethiopic numerals. It contains distinct glyphs for the the initial, medial, and final form of every digit, plus an isolated form which gets used when a digit stands alone. In its Glyph Substitution table, the test font uses a Glyph Composition/Decomposition feature to select the correct shape depending on its context. To achieve this effect, the feature invokes lookups for Chaining Contextual Substitution. In the test rendering, you should see continuous strokes; only the the first and the last digit of each number should have side strokes. If you can see small side strokes also at interior digits, it’s a sign that your text rendering engine is broken.