Add rationale for a couple glyf table checks

com.google.fonts/check/glyf_unused_data
com.google.fonts/check/points_out_of_bounds
On the Open Type Profile.

(PR #4570)

CHANGELOG.md

@@ -34,6 +34,8 @@ A more detailed list of changes is available in the corresponding milestones for
   - **[com.google.fonts/check/family/equal_unicode_encodings]:** Added rationale, even though this is a questionable check, which we may simply deprecate, as we're not sure why would we expect what it checks. (PR #4570)
   - **[com.google.fonts/check/family/equal_font_versions]:** Added rationale. (PR #4570)
   - **[com.google.fonts/check/font_version]:** Added rationale. (PR #4570)
+  - **[com.google.fonts/check/glyf_unused_data]:** Added rationale. (PR #4570)
+  - **[com.google.fonts/check/points_out_of_bounds]:** Added rationale. (PR #4570)
 
 
 ## 0.12.0a2 (2024-Feb-21)

Lib/fontbakery/checks/opentype/glyf.py

@@ -7,6 +7,13 @@
 
 @check(
     id="com.google.fonts/check/glyf_unused_data",
+    rationale="""
+        This check validates the structural integrity of the glyf table,
+        by checking that all glyphs referenced in the loca table are
+        actually present in the glyf table and that there is no unused
+        data at the end of the glyf table. A failure here indicates a
+        problem with the font compiler.
+    """,
     conditions=["is_ttf"],
     proposal="legacy:check/069",
 )
@@ -45,6 +52,12 @@ def com_google_fonts_check_glyf_unused_data(ttFont):
 @check(
     id="com.google.fonts/check/points_out_of_bounds",
     conditions=["is_ttf"],
+    rationale="""
+        The glyf table specifies a bounding box for each glyph. This check
+        ensures that all points in all glyph paths are within the bounding
+        box. Glyphs with out-of-bounds points can cause rendering issues in
+        some software, and should be corrected.
+    """,
     proposal="https://github.com/fonttools/fontbakery/issues/735",
 )
 def com_google_fonts_check_points_out_of_bounds(ttFont, config):