Thank you both for your responses. Yes, U+2502 or U+2503 would achieve the desired effect for which I devised U+E700 STAFF without resorting to the Private Use Area.
The only reason for my not using one of those was that I was unaware of those codes as such. An interesting point is that they appear to be usable with fonts which have descenders yet still fill the entire height of the font. I suppose that when I had, some time ago, when looking through what Unicode offers, in a general context, not looking for the STAFF effect at that time, seen the box drawing characters I thought of those characters in the context of the character set of the old PET computer from the 1970s and of the way that some software on older non-graphics terminals on mainframe computers makes an attempt at message windows using such characters to construct boxes. Indeed, an interesting footnote to U+2502 states = Videotex Mosaic DG14. I cannot quite remember what Videotex was. I remember Videotext (with a t at the end) and seem to remember that Videotex (no t at the end) was a different system, possibly from the USA or maybe France. There was also a system which started called NAPLPS, which was an acronym for something like North American something and the word Presentation was in it, though I forget the exact acronym derivation. I was unaware of the VDMX table and so had a look at http://www.yahoo.com and found a couple of useful documents. However, VDMX appears to refer specifically to OpenType rather than ordinary TrueType. My reason for including the STAFF character, the intended effect of which I can now produce using U+2502 or U+2503, was that, being fairly new to producing fonts and just, thus far, using the Softy editor to produce ordinary TrueType fonts, I had noticed, when trying it out in 2002, that if I produce a font with a b c d e f then the font displays with lines packed togather, yet that if I then add g the line spacing for all lines increases, even if there is no g in that line. So I reasoned that the system might scan through a font when it is loaded and decide upon the lowest point for the whole font and then proceed on that basis. Now, in defining Quest text I wanted to have the possibility of accents on capital letters and descenders such as y and g and always look clear, so I decided effectively to lock some leading into the font and set the maximum height right from the start. Features of Quest text are that it is designed so that characters are produced directly from drawings in the Softy editor, not from template graphics, and that Quest text is designed, as far as possible, by the application of a set of rules, such as that verticals are all 256 font units wide, with both edges at a font unit value which is a multiple of 256 and that horizontals are all 168 font units in vertical height with one edge at a font unit value which is a multiple of 256, corners which are curved are curved with a single Bézier curve which has an action length, as I call it, of 128 font units in both horizontal and vertical directions. Some characters, such as x and k are exceptions to the general rules, yet Quest text is largely made up of horizontals and verticals, including for letters such as A O e and s. The idea is that hopefully Quest text will be very clear at both 12 point and 18 point and that, as point size increases, it will display its artistic look. At 300 point, Quest text looks smooth and rounded with an elegant combining of wider verticals with narrower horizontals, almost as if drawn with a pen with a nib 256 font units wide and 168 font units high. The rules do produce the effect though that capitals look lighter than lowercase letters as they are overall wider and yet use the same width verticals. I am wondering whether to consider that a fault or a feature! :-) An important part of the development process of Quest text is to display some text at 12 point in WordPad, make a Print Screen graphic and paste it into Paint and then study the graphic at 8x magnification. Hopefully Quest text combines great clarity with an artistic look. William Overington 13 March 2003