<p><span style="font-size:18px;">Erik Carvalhal Miller wrote as follows.</span></p><p> </p><p><span style="background-color:rgb(255,255,255);color:rgb(85,85,85);font-family:helvetica, arial, verdana, sans-serif;font-size:18px;"><span style="-webkit-text-stroke-width:0px;display:inline !important;float:none;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;orphans:2;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;">> Although the angle brackets have Unicode names containing the word “mathematical” and reside in the Miscellaneous Mathematical Symbols-A block, I was thinking of their linguistic use for denoting characters qua characters.</span></span></p><p> </p><p><span style="background-color:rgb(255,255,255);color:rgb(85,85,85);font-family:helvetica, arial, verdana, sans-serif;font-size:18px;"><span style="-webkit-text-stroke-width:0px;display:inline !important;float:none;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;orphans:2;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;">I was unaware of that usage. Thank you for explaining.</span></span></p><p> </p><p><span style="background-color:rgb(255,255,255);color:rgb(85,85,85);font-family:helvetica, arial, verdana, sans-serif;font-size:18px;"><span style="-webkit-text-stroke-width:0px;display:inline !important;float:none;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;orphans:2;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;">> The single missing‐glyph glyph you originally saw between them was the fallback display I expected in accordance with the Standard.</span></span></p><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"> </div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"><span style="font-size:18px;">> Note that UTS #51 encourages any implementation that supports emoji tag sequences but has difficulty with a particular sequence to fall back by displaying the base emoji either followed by or overlaid by a “missing‐emoji glyph”;</span></div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"> </div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"><span style="font-size:18px;">That situation is because the character that is used for the base character of the tag sequence can also be used on its own for its original meaning. I am not suggesting, (within the limits of the usage being discussed here as anyone may use a Private Use character for their own purpose) using U+10FFFD other than as the base character for a tag sequence. If the OpenType font recognizes a particular sequence of the base character and some tag characters as if a ligature and displays a substituted glyph accordingly, then no glyph for U+10FFFD will be displayed. So a display of a glyph for U+10FFFD will only be displayed if the font in use does not recognize a particular sequence of the base character and some tag characters. So, for example, if a font with the suggested glyph for U+10FFFD and recognizing, say, twenty sequences of the base character and some tag characters, is used to display some text, then the font could respond according to whatever sequences are in the text that is displayed, substituting a glyph or displaying U+10FFFD as appropriate for each sequence encountered.</span></div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"> </div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"><span style="font-size:18px;">A font with visible glyphs for tag characters will be helpful for composing sequences and could also be useful for finding the meaning of sequences that are not supported by any font available to the particular end user.</span></div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"> </div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"><span style="font-size:18px;">> since in this case itʼs not likely that the PUA character would even be recognized as an emoji, the fallback you saw is the best‐case scenario one can expect in the absence of a private‐use agreement.</span></div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"> </div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"><span style="font-size:18px;">Well, I was not restricting myself to emoji in applying the technique of using U+10FFFD followed by a sequence of tag characters of which the final one is a CANCEL TAG. Emoji sometimes, yet other things too.</span></div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"> </div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"><span style="font-size:18px;">I had in mind a font where the glyph for U+10FFFD would be a rectangle with within the rectangle the top half of a question mark and instead of a dot a horizontal arrow pointing to the right as viewed by the viewer.</span></div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"> </div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"><span style="font-size:18px;">I consider that the phrase "private agreement" in The Unicode Standard is, well, not. the whole situation, as it is perfectly possible for on person to produce and publish a document declaring some meanings and/or glyphs. So while for anyone else to apply those meanings and/or glyphs does imply at least a tacit, temporary, like watching a science fiction movie suspension of disbelief, sort of agreement, it is not the almost formal contractual situation that The Unicode Standard could be reasonably thought to be writing about.</span></div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"><span style="font-size:18px;"> </span></div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"><a target="_blank" rel="noopener noreferrer" href="https://www.unicode.org/versions/Unicode15.0.0/ch23.pdf"><span style="font-size:18px;">https://www.unicode.org/versions/Unicode15.0.0/ch23.pdf</span></a><span style="font-size:18px;"> page 23 of the PDF document</span></div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"> </div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"><span style="font-size:18px;">William Overington</span></div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"> </div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"><span style="font-size:18px;">Monday 29 April 2024</span></div><div style="-webkit-text-stroke-width:0px;background-color:rgb(255, 255, 255);border:0px;box-sizing:border-box;color:rgb(85, 85, 85);font-family:helvetica, arial, verdana, sans-serif;font-size:14px;font-style:normal;font-variant-caps:normal;font-variant-ligatures:normal;font-weight:400;letter-spacing:normal;margin:0px;orphans:2;padding:0px;text-align:start;text-decoration-color:initial;text-decoration-style:initial;text-decoration-thickness:initial;text-indent:0px;text-transform:none;white-space:pre-line;widows:2;word-spacing:0px;"> </div><p> </p>