ElyMark: task boxes are drawn at text size on the first line (R2.14)

tests/scripts/mark-content.sh

@@ -62,6 +62,10 @@ for step in ("visual", "themed", "preview"):
     for key, value in [("title", "Title"), ("heading", True), ("inline", True), ("display", True), ("tasks", 2),
                        ("cells", 2), ("notes", 1), ("font", True), ("editors", 1)]:
         want(step, key, value)
+    # The task box: text-sized, centred on its line.
+    width, height, off = seen[step]["box"]
+    if abs(width - 1) > 0.01 or abs(height - 1) > 0.01 or abs(off) > 1:
+        sys.exit(f"FAIL: {step} task box is {seen[step]['box']}")
     blocks = seen[step]["blocks"]
     if [block["language"] for block in blocks] != languages:
         sys.exit(f"FAIL: {step} blocks are {blocks}")