Yes it is expected. And in fact very common in Unicode since long (there are in fact many "Mn" marks with combining class 0, this is not just for one script).
A combining class 0 DOES NOT mean that the character will not be a non-spacing mark (or that it will be spacing), but just that it blocks reorderings under standard normalizations and for recognizing canonical equivalences. (see for example CGJ which also has combining class 0 and which is used mostly to insert such blocking behavior, without having any real semantic meaning by itself ; once the normalization step has been done, it can be discarded from the input stream in renderers or collators, except for special purposes like rendering CGJ with its own visible glyph in some "visible controls" edit mode) Technically CGJ is not "Mn" (not a combining mark) but a "formatting control", but it still participates to the grouping of "default grapheme clusters", as if it was a combining mark -- and for most parts, it is an artefact of the encoding in the UCS, and considered foreign to the script by native writers, but it is also needed for compatibility reasons. However, in many scripts, there exists true combining marks (Mn) that have combining class 0 (i.e. whose relative ordering in the encoded stream is semantically significant when they are used in conjunction with other reorderable combining marks). General categories are very fuzzy in fact ; this is an old property with lots of caveats if you want to use this property alone, and there are newer orthogonal properties for more precise behaviors for specific algorithms. General categories however have been kept for compatibility reason with early implementations (when the UCS was much less populated and much less languages were supported, and many algorithms were still not standardized because the best practices were still not known, or not well understood, or not yet decided and documented to support these languages). You'll certainly see in this list other responses giving another point of view. 2013/5/18 Matt Ma <[email protected]> > Hi, > > U+0F76 is a non-spacing combing mark (Mn) but its combing class value is > defined as 0. Is this expected? The specialty of the character is that it > is a composition of two combining marks, U+0FB2 and U+0F80. > > Same question goes for U+0F73, U+0F75, U+0F77, U+0F78, and U+0F79. > > Thanks and regards, > Matt >
