lInternalLeading (LONG)
The amount of space which, when subtracted from lMaxAscender, gives a font-design dependent, but glyph-set independent, measure of the distance above the baseline that characters extend. This calculation approximates the visual top to a row of characters without actually looking at the characters in the row.
For optimum results, this field should be used by applications to position the first line of a block of text by subtracting it from lMaxAscender and positioning the baseline that distance below whatever is above the text.
Note: This does not guarantee that characters will not overwrite information above them, but does give a font designer's view of where to place the text. Collision should be tested for, and additional space allocated if necessary.