[font] Docs

src/hb-font.cc

diff --git a/src/hb-font.cc b/src/hb-font.cc
index c3a4c4b..8a43ceb 100644
--- a/src/hb-font.cc
+++ b/src/hb-font.cc
@@ -1061,7 +1061,8 @@
  * @glyph_stride: The stride between successive glyph IDs
  *
  * Fetches the nominal glyph IDs for a sequence of Unicode code points. Glyph
- * IDs must be returned in a #hb_codepoint_t output parameter.
+ * IDs must be returned in a #hb_codepoint_t output parameter. Stopes at the
+ * first unsupported glyph ID.
  *
  * Return value: the number of code points processed
  *