Checks for Adobe Fonts (formerly known as Typekit).
Fonts have consistent Units Per Em?
While not required by the OpenType spec, we (Adobe) expect that a group of fonts designed & produced as a family have consistent units per em.
Letters in font have glyphs that are not empty?
Font language, script, and character set tagging approaches typically have an underlying assumption that letters (i.e. characters with Unicode general category ‘Ll’, ‘Lm’, ‘Lo’, ‘Lt’, or ‘Lu’, which includes CJK ideographs and Hangul syllables) with entries in the ‘cmap’ table have glyphs with ink (with a few exceptions, notably the Hangul “filler” characters).
This check is intended to identify fonts in which such letters have been mapped to empty glyphs (typically done as a form of subsetting). Letters with empty glyphs should have their entries removed from the ‘cmap’ table, even if the empty glyphs are left in place (e.g. for CID consistency).