Consider also that the BMP is almost full, the remaining few holes are kept for isolated characters that may be added to existing scripts, or permanently reserved to avoid clashes with legacy softwares using simple code remappings between distinct blocks, or to perform simple case conversions (e.g. in Greek) for internal purposes (these positions are not interoperable and may clash with future versions of the UCS and I18n tools/libraries like ICU)
You should abstain using any currently unassigned positions in the existing Unicode blocks: use PUA if you have nothing else; there are plenty of space available, in the BMP (most common usage in fonts that need to map additional glyphs) or in the two last planes. The PUA block in the BMP is large enough for most apps and almost all fonts that need private glyphs for internal purposes, or for still unencoded characters or for your own encoded variants such as slanted symbols, rotated symbols, inverted symbols, or symbols with multiple sizes, or at different positions on the musical score, or using distinct styles (e.g. between different players or singers, or various symbols for percusive instruments or specific intruments, or extra annotations). Many new symbols have been encoded first as PUAs in early fonts used to create proposals (then rendered to a PDF, or embedded fonts in a rich text document, or webfonts loaded from static versioned URLs on a repository like GitHub or on a public cloud). Later the proposal passed the early steps for reviewing the repertoire and choosing more relevant positions, then characters were encoded and standardized and these fonts were updated to map their glyphs to not just their existing PUAs but also the nex standard positions (or encoded variants) 2017-05-02 2:27 GMT+02:00 Richard Wordingham via Unicode < unicode@unicode.org>: > On Mon, 1 May 2017 23:03:53 +0000 > Michael Bear via Unicode <unicode@unicode.org> wrote: > > > “Rather than using "unused code positions", I would always recommend > > to use some of the Private Use code points.” Consider it done. > > > > “What is the intended usage of your font? Music score > > applications? others?” I am simply going to make a series of full > > Unicode fonts (which, due to the 65,535-character limit in fonts, > > each of the 3 fonts covers different planes: The first font does the > > BMP, > > How much margin do you have for the BMP? There are a fair few > variation sequences, on top of all the contextual forms and conjuncts. >