The rationale is most probably the same for ALL existing mathematical "letters" : they are the same letters, but their specific encoding is done so that it explicitly specifies a rendering style which is significant in mathematical notations, where they are not really letters but formal symbols with a very precise visual identity to differentiate them between each other.
The encoding in U+1D52x is probably too precise for something else than just math notations. The new encoding in U+AB3x is necessarily for somthing else than maths, otherwise it should have not occured. Symbols encoded in U+1Dxxx are not suitable for anything else than notations of mathemetical or scientific formulas or diagrams. But then, why some letters were unified with other existing letters in other blocks? can you explain the few holes in the encoded math alphabets for something else than just compatibility with prior texts? 2013/9/10 Asmus Freytag <asm...@ix.netcom.com> > Good question, Jean-François. > > I seem to recall that typographers may make a distinction between > "black-letter" and "fraktur" forms, but even if they, the differences are > typographical, not essential. For the purpose of *character* encoding, one > would need to make a very strong rationale for disunifying these. > > This rationale is absent in document WG2 N3907 that requests these > characters. > > Therefore, it seems these two additions should not have been made. > > A./ > > > On 9/10/2013 2:23 AM, Jean-François Colson wrote: > >> Version 7 of Unicode includes the following two letters: >> ꬲ AB32 LATIN SMALL LETTER BLACKLETTER E >> ꬽ AB3D LATIN SMALL LETTER BLACKLETTER O >> >> There already were the following two: >> 𝔢 1D522 MATHEMATICAL FRAKTUR SMALL E >> 𝔬 1D52C MATHEMATICAL FRAKTUR SMALL O >> >> For these, there’s an annotation: >> @ Fraktur symbols >> @+ This style is sometimes known as black-letter. >> >> What’s the difference between U+AB32 and U+1D522? >> Between U+AB3D and 1D52C? >> >> >> >> > >
