Tested what user agents are actually doing with value on inputs.
Test case: https://carmacleod.github.io/playground/value-attr-tests.html
TL/DR: They are mostly doing what HTML-AAM told them to do.

button type inputs: value maps to accessible name (and accessible value?) (and is added as visible text content).
Don't want it mapped to aria-label. Accname doesn't seem to support this? Unless it's covered in step 2D or maybe 2G?
numeric type inputs: value maps to accessible value (and is added as visible text content or thumb position).
Ok to map to aria-valuenow because aria-valuenow in CORE-AAM is the same.
text type inputs: value maps to accessible value (and is added as visible text content) as long as correct format is used (password maps to dots).
Would be ok to map to aria-valuetext (assuming ARIA role supports attr) because aria-valuetext in CORE-AAM is the same.
other: cannot set value for file input (value is "No file selected" initially, and is only set in UI), and checkbox/radio value is only used to represent the input for form submission

button type inputs: value maps to accessible name (and is added as visible text content).
numeric type inputs: value maps to accessible value (and is added as visible text content or thumb position).
text type inputs: value maps to accessible value (and is added as visible text content) as long as correct format is used.
Except for password, date, time, color (these are set in the UI, but not mapped in the a11y tree - opened FF bug).
other: as above

button type inputs: value maps to accessible name (AXLabel for image button, AXTitle for the others) (and is added as visible text content).
numeric type inputs: value maps to accessible value (and is added as visible text content or thumb position).
(For slider, value is mapped on thumb, not on slider itself).
text type inputs: value maps to accessible value (and is added as visible text content) as long as correct format is used (password maps to dots).
other: as above, except that checkbox/radio accessible value is set to 0 or 1 based on state

@joanmarie Are the ATK mappings basically the same as Chrome/Edge/Win? i.e. the mappings that HTML-AAM specifies?

value should map to aria-valuenow for input[type=range] #314

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