Table headers don't support subscript or superscript

[astreater]

As a content publisher publishing tables of mathematical or scientific data, I need to be able to format characters as superscript and subscript in table headers so that I can express chemical and mathematical symbols.

Quite a specific use case but for things like mg/m³ or SO₂, govspeak doesn't seem to allow this in headers.

Example:

`	Fuel sulfur % by mass	ELV SO2 (mg/m3) at 3% O2	ELV SO2 (mg/m3) at 15% O2
0.2%	350	120
0.5%	850	290
1.0%	1700	570	`

The desired output is something like the below:

Fuel sulfur % by mass	ELV SO2 (mg/m3) at 3% O2	ELV SO2 (mg/m3) at 15% O2
0.2%	350	120
0.5%	850	290
1.0%	1700	570

Raised on behalf of Esther Woods (Content Designer): https://gds.slack.com/archives/CAB4PSQKW/p1612529109158600

[estherwoods]

This was raised from a Whitehall publisher query: https://govuk.zendesk.com/agent/tickets/4455960

[kr8n3r]

as discussed a workaround for the time being is to use unicode characters

• either ₂, ₃ and ³ as part of the text like ELV SO₂ (mg/m₃) at 3% O₂

• or copy ₂, ₃ and ³ to clipboard and use like "ELV SO₂ (mg/m³) at 3% O₂"