HeaderDisplayFunction

is an option for Dataset that specifies a function to apply to headers before displaying them.

Details

The setting for HeaderDisplayFunction can be any pure function.
With the option HeaderDisplayFunctionf, the specified function will be applied to all headers in the dataset before displaying them.
With the option HeaderDisplayFunctionf, the displayed header is given by f[header,position,dataset].
The settings for HeaderDisplayFunction can be given as follows to apply separately to different items:
spec apply spec to all headers

{spec₁,spec₂,…,spec_n} apply spec_k to headers at dataset level k

${spec_(1),spec_(2),...,spec_(n), rules}$ also allow explicit rules for individual headers
The spec_k can have the following forms:

	{s₁,s₂,…,s_n}	use s₁ through s_n; then use defaults
	{{c}}	use c in all cases
	{{c₁,c₂}}	alternate between c₁ and c₂
	{{c₁,c₂,…}}	cycle through all c_i
	{s,{c}}	use s, then repeatedly use c
	{s₁,{c},s_n}	use s₁, then repeatedly use c, but use s_n at the end
	{s₁,s₂,…,{c₁,c₂,…},s_m,…,s_n}	use the first sequence of s_i at the beginning, then cyclically use the c_i, then use the last sequence of s_i at the end
	{s₁,s₂,…,{},s_m,…,s_n}	use the first sequence of s_i at the beginning and the last sequence at the end

Rules have the form ispec, where i specifies a position in the dataset.
Positions can be patterns.
The position of a header can be read at the bottom of a dataset when you hover over the header.
If the left-hand side of a rule is not a list, the setting is applied to any position that contains the left-hand side as a key or index.

open allclose all

Make all headers lowercase:

The value of HeaderDisplayFunction must be an explicit pure function. Other values will have no effect:

Use an explicit pure function:

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	spec	apply spec to all headers
	{spec₁,spec₂,…,spec_n}	apply spec_k to headers at dataset level k
	${spec_(1),spec_(2),...,spec_(n), rules}$	also allow explicit rules for individual headers