eldoc-argument-case is a variable defined in `eldoc.el'.
Its value is

  • This variable is obsolete since 25.1.

Case to display argument names of functions, as a symbol.
This has two preferred values: `upcase' or `downcase'.
Actually, any name of a function which takes a string as an argument and
returns another string is acceptable.

Note that this variable has no effect, unless
`eldoc-documentation-function' handles it explicitly.

You can customize this variable.