Translate a 0-based key index (e.g. 0 for the '1' key, 1 for '2',
etc.) into the new selectedDimension value, or null when the
key falls past the available navigable dimensions.
Returns the key index unchanged on success — the index is already
the navigable position. On failure, returns null plus the count of
navigable dims so the caller can include it in a "not available"
message.
Translate a 0-based key index (e.g. 0 for the '1' key, 1 for '2', etc.) into the new
selectedDimensionvalue, ornullwhen the key falls past the available navigable dimensions.Returns the key index unchanged on success — the index is already the navigable position. On failure, returns
nullplus the count of navigable dims so the caller can include it in a "not available" message.