Cut the comments back to the genuinely subtle ones

text.go

@@ -27,12 +27,10 @@ type textFace struct {
 	ascent int
 	cache  map[rune]*glyph
 
-	// Where a line of text starts and stops as far as the eye is concerned: the
-	// top of a digit or capital, down to the baseline. The cell is taller at
-	// both ends, reserving space above for accents nothing here uses and below
-	// for descenders, which hang past the line without being read as part of
-	// it. Laying out by the cell therefore puts visibly more air around text
-	// than around a bordered box the same distance away.
+	// The line as the eye reads it: top of a digit down to the baseline. The
+	// cell is taller at both ends, holding accent space nothing here uses and
+	// descenders that hang past the line without being read as part of it, so
+	// laying out by the cell puts more air around text than around a box.
 	capTop int
 	lineH  int
 }