Underscore Character vs. Underlining

[Gerry Kowarsky]

Because I have a new laptop with Windows XP, I have been testing a variety of different fonts to see how much of difference ClearType makes. One of the documents I experimented with includes several lines made up of underscores and underlined text. In the original, the text seems to float above continuous lines. As I experimented, I was struck with how much variation there is among fonts on the placement and thickness of the underscore character. In some fonts, underscores are indistinguishable from underlining. In others, the underscore is higher or lower, thicker or thinner, than underlining.

As I thought about the variation, I came up with a good reason for the underscore to differ from underlining. Without a difference, it's difficult tell whether an underlined URL contains spaces or underscores. I'm not sure this is the reason for the variation I found, however. It is easier to distinguish between underlined spaces and underscores in
Times New_Roman than in the more recent Verdana. In Verdana, all you can go by is
the character_width (a space precedes "character," an underscore follows it).

I know it is possible to specify underscore width and position in an AFM file. Does anyone know what happens if these parameters are not set? Could the variation I found result from the absence of a choice rather than a choice? If not, what other reasons might there be to distinguish between the underscore and underlining?

[Michael Rowley]

Gerry:

'I know it is possible to specify underscore width and position in an AFM file'

There is no AFM file for a TT font, neither is there for a T1-flavoured OT font (OTF). Since the difference between an underscore character and underlining, the character (005F) is presumably specified by the type designer, unless anyone's interfered with it. The distance and style of underlining is specified by the designer of the program (Word etc.).