Given the "squiggle" below letters are actually gien distinctive semantics, I think it should be encoded a combining character (to be written not after a "superscript" but after any normal base letter, possibly with other combining characters, or CGJ if needed because of the compatibility equivalence. That "squiggle" (which may look like an underscore) would haver the effect of implicity making the base letter superscript (smaller and elevated). It would have probably a "combining below" class.
In that case U+2116 № is perfectly encodable, but still distinct from <N,o,COMBINING ABBREVIATION MARK> because "№" does not require this mark (so there's no problem of stability with canonical equivalences, even if this creates new possible confusable pairs when either the mark is used after a normal letter: the risk of confusion only exists for "№" which is a legacy non-decomposable ligature but that has an existing compatibility equivalence, just like all other subscript letters). In that case we have other ways to note *semantically* any abbreviations using distinctive final letters (including for N<os> abbreviating "Numeros", M<me> for "Madame", M<le> for "Mademoiselle", M<rs>, M<gr> for Monseigneur, P<r> abbreviating "Professor"/"Professeur", or f<n> abbreviating "function"). Notes: * The <o> and <os> are also used in French, instead of <n> or <ns> to abbreviate a "-tion" or "-tions" suffix (which derives from Latin "-tio" or "-tios"). But I've also seen other abbreviation marks used for "-tion" and "-tions". * we also have in Unicode distinctive codes for dots used as abbreviation marks (they are not combining, but still encoded distinctly from the regular punctuation full stop), and for the mathematical binary dot operator, or the decimal separator, or for implicit mathematical operators that don't mark anything (i.e. invisible and zero-wdth) but that only break grapheme clusters and prohibit formation of discretionary ligatures). Medieval books or mails contained lot of abbreviation marks due to the cost of paper (or parchment): texts were then frequently "packed" using combining abbreviation marks in various positions (generally above or below). The Germanic "Fraktur e" was a remnant of this old practice, inherited from phonetic annotations added on top of Greek, Hebrew and Arabic, which later turned into an "umlaut" that Unicode unified with the diaeresis, even if it breaks the historic link to the letter Latin "e" used like an abreviation mark or Hebrew vowel point in Fraktur (I think that the history of the "Germanic Fraktur e" is highly linked to the influence of Hebrew in today's Germany, or Greek in today's Eastern and Southern Europe with some Slavic traditions in Cyrillic connected to religious traditions in Greek). The introduction of interlinear annotations in Greek was also margely influenced by Hebrew and Arabic (which however did not turn these marks into plain letters and avoided the formation of complex ligatures like in Indian Brahmic scripts), but was the base of the interlinear notation of actual phonetic. Even the combining accents in French were created after an initial step using ligatures of plain letters, before people started to replace these ligatures by some unstable combining marks (initially not distinguished) then turned them into plain distinctive accents which became the de facto standard (made the offical orthography only very late: before that there was a wide variation between those that wanted to distinguish phonetics, using different accents, but now French tends to simplify this set: the circumflkex in French was an abreviation mark for the unwritten letter "s" which initially was more like the tilde, i.e. a turned small "s"). The German umlaut written like a diaeresis is also very new (only after the abandonment of the Fraktut alphabet where the "e" just looked like two thick vertical strokes Le dim. 28 oct. 2018 à 10:41, arno.schmitt via Unicode <unicode@unicode.org> a écrit : > Am 28.10.2018 um 09:13 schrieb Richard Wordingham via Unicode: > > The notation is a quite widespread format for abbreviations. the > > first letter is normal sized, and the subsequent letter is written in > > some variety of superscript with a squiggle underneath so that it > > doesn't get overlooked. I have deduced that this is not plain text > > because there is no encoding mechanism for it. For example, our > > lecturers would frequently use this treatment to abbreviate function > > as 'fn' with the 'n' superscript and supported by a squiggle below > > sitting on the baseline. The squiggle below has meaning; it marks the > > word as an abbreviation. > > > > Richard. > > Looks to me like U+2116 № NUMERO SIGN > which perhaps should not have encoded, > since we have both U+004E LATIN CAPITAL LETTER N and > U+00BA º MASCULINE ORDINAL INDICATOR > > Arn0 >