Hi,
in a sample of Austrian newspapers 1850-1911 different styles of decimal points appear:
1) 21
˙3 dot aligned with top of the figures, e. g. temperature
2) 21˙³³ dot aligned with top of the figures followed by superscript, e. g. exchange rates
3) 17·12, 17·— dot aligned near the hight of a dash, e. g. prices
4) 21.3 dot aligned with baseline
5) 21.₇₇ dot aligned with baseline followed by subscript, e. g. exchange rates
Assuming a moderate level of transcription, i. e. as near as possible to the original typography and orthography but no use of PUA, it's questionable which codepoints to use.
Here are the candidates I found so far in Unicode Version 12:
'.' U+002E FULL STOP (Other_Punctuation)
'·' U+00B7 MIDDLE DOT (Other_Punctuation)
'˙' U+02D9 DOT ABOVE (Modifier_Symbol)
'·' U+0387 GREEK ANO TELEIA (Other_Punctuation)
'᛫' U+16EB RUNIC SINGLE PUNCTUATION (Other_Punctuation)
'․' U+2024 ONE DOT LEADER (Other_Punctuation)
'‧' U+2027 HYPHENATION POINT (Other_Punctuation)
'∙' U+2219 BULLET OPERATOR (Math_Symbol)
'⋅' U+22C5 DOT OPERATOR (Math_Symbol)
'⸱' U+2E31 WORD SEPARATOR MIDDLE DOT (Other_Punctuation)
'⸳' U+2E33 RAISED DOT (Other_Punctuation)
'・' U+30FB KATAKANA MIDDLE DOT (Other_Punctuation)
'ꞏ' U+A78F LATIN LETTER SINOLOGICAL DOT (Other_Letter)
MIDDLE DOT appears frequently in current and old typography and is available in most fonts.
But I hesitate to use DOT ABOVE, because it's a modifier symbol.
In a text format allowing activation of OT features that's a possible solution.
I wonder a little bit, that subscript and superscript code points exist in Unicode, but no sub/sup punctuation. Did I miss something?
Apart from the appropriate encoding the second question is, which features to use in case of font reconstruction. In case 2) the figures after the dot are not positioned like the usual sups but aligned at the top, and in case 5) the bottom of the subs is at baseline.
Comments
re. U+02D9 DOT ABOVE this might work, but would depend on the height in particular fonts. This character is used for Mandarian Chinese tone 5, which is a high tone. I'd be inclined to align the dot to the top of the cap height, but some people might make it higher.
With the possible exception of the mid dot, My instinct would be to encode most of these using just the standard 0x002E codepoint with subscript or superscript features applied.
From the annotation in Unicode
DUPLOYAN AFFIX HIGH DOT
French number thousands
French suffix -eur
Romanian affix trans-/-lui
not Romanian hundreds - use 0307
combining dot above and 0308̈ combining
diaeresis
→ 02D9 dot above
The vertical alignment is interesting. Superscript numbers were used very early in historic typography for footnotes. But they used smaller fonts and raised them by non printing material. Later they casted extra ones for speed of typesetting, and also special use in fractions, tables, calendars, train schedules.
In current fonts and revivals many don't have subscripts and the alignment is also different. Hard to find good fonts for transcriptions.
Some examples:
U+2E33 RAISED DOT according to Unicode is "glyph position intermediate between U+002E . [full stop] and U+00B7 · [middle dot]".
Unicode has a problem with dots. It encodes quite a lot of individual and patterns of dots in various scripts, and the UTC is very hesitant to encode any more. So whenever someone finds a new use of a dot and proposes to encode it, the standard response now is 'Couldn't you use one of the existing dot characters?' So it's very likely that, over time, various dots will accumulate additional annotations and recommended uses, regardless of in which block they are encoded.