Christoph Päper had asked:
there has been a tradition (in handwritten text more than in print) of writing "mm" as only one "m" with a macron above. I can't find any such character in Unicode,
You could of course build something similar with "m"+U+0305 to resemble the look, but that won't become "mm" (just "m" or "m¯") after a conversion to e.g. ISO-8859-1.
This depends on the program used to do the conversion. When you want to properly handle a particular writing tradition, you cannot rely on off- the-shelf tools, unaware of the particular requirements. Kenneth Whistler wrote:
Handwritten forms and arbitrary manuscript abbreviations should not be encoded as characters. The text should just be represented as "m" + "m". Then, if you wish to *render* such text in a font which mimics this style of handwriting and uses such abbreviations, then you would need the font to ligate "mm" sequences into a *glyph* showing an "m" with an overbar.
This will not work, as all 'mm' occurences are not written as m-overbar. E. g., G. Keller's "Die drei gerechten Kammacher" <http://gutenberg.spiegel.de/keller/seldwyla/kammachr/kammachr.htm> could not be written with m-overbar, as the two "m" characters belong to different syllables; in modern orthography, you would write "Kammmacher", or -- if you wish so -- Ka<m-overbar>macher. So, if you want to render m-overbar, you would have to mark it in text, and the only way Unicode has to offer, is U+006D U+0304. (I would not use U+0305, as this is too high and too wide. I reckon, a good rendering engine should adapt U+304's width to the pertenent base character's width.)
To do otherwise, either representing the plain text content as <m, combining-macron> or with a newly encoded m-macron character, would just distort the *content* of the text, which is what the character encoding should be about.
It would not distort the content of the text for readers that are accustomed to this sort of abbreviation -- no more than the spelling "i. e." would distort the content of "that is" for an average English reader.
If and only if an m-macron became a part of the accepted, general orthography of German
It used to be. Markus Scherer wrote:
I can confirm the use of m+overline from my family, [...] I always considered those personal variations, "font styles" if you wish.
Now I know that the m+overline was used elsewhere,
In German handwriting (Kurrent), the sequences of the letters "m", "n", "u", and "i" look very confusing: an "ü" is written exactly as "ii" would be (if it ever were) written; the "u" needs a hook above (akin to U+0306, but it is an intrinsic part uf the Kurrent "u" glyph) to distinguish it from the "n", and "mm" cannot be distinguished from "nnn" (which came into German orthography only in 1996, so there was no ambiguity when Kurrent was widely used). Try to read, e. g., the penultimate word of the first line of H. Carossas poem in <http://www.e-welt.net/BfdS/schrift.htm#lese>: it's "immer" (and the penultimate word of the 2nd line reads "Brunnens"). This problem was even worse with the medieval Textura font. Hence, medieval scribes developed a rich set of abbreviations, including the overbar for an omitted "m" or "n". The latter has survived into German handwriting, at least until the 1st half of the 20th century. Best wishes, Otto Stolz PS. Never write "Hawaii" in German Kurrent ;-)
