Back out change #218

See discussion in #217 and googlefonts/ufo2ft#760

versions/ufo3/fontinfo.plist.md

@@ -286,7 +286,7 @@ Records should have a unique `nameID`, `platformID`, `encodingID` and `languageI
 | postscriptSlantAngle | integer or float | Artificial slant angle. This must be an angle in counter-clockwise degrees from the vertical. This value is *not* the same as the italic angle. Font authoring tools may use this value to set the FontMatrix in Type 1/CFF table. |
 | postscriptUniqueID | integer | A unique ID number as defined in the Type 1/CFF specification. |
 | postscriptUnderlineThickness | integer or float | Underline thickness value. Corresponds to the Type 1/CFF/post table `UnderlineThickness` field. |
-| postscriptUnderlinePosition | integer or float | Underline position value. Corresponds to the Type 1/CFF table `UnderlinePosition` field. The post/CFF2 table `UnderlinePosition` should be calculated from this value by adding half of the `postscriptUnderlineThickness` to `postscriptUnderlinePosition`. |
+| postscriptUnderlinePosition | integer or float | Underline position value. Corresponds to the Type 1/CFF/post table `UnderlinePosition` field. *Note: This value is ambiguous as post/CFF2 defines this position from the top, and Type 1/CFF defines it from the middle of the underline. The result of this value depends on which definition a compiler uses.* |
 | postscriptIsFixedPitch | boolean | Indicates if the font is monospaced. An authoring tool could calculate this automatically, but the designer may wish to override this setting. This corresponds to the Type 1/CFF `isFixedPitched` field |
 | postscriptBlueValues | list | A list of up to 14 integers or floats specifying the values that should be in the Type 1/CFF BlueValues field. This list must contain an even number of integers following the rules defined in the Type 1/CFF specification. |
 | postscriptOtherBlues | list | A list of up to 10 integers or floats specifying the values that should be in the Type 1/CFF OtherBlues field. This list must contain an even number of integers following the rules defined in the Type 1/CFF specification. |