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A general description is here.
‘curlGetHeaders()’ has two new arguments, ‘timeout’ to specify the timeout for that call (overriding ‘getOption("timeout")’) and ‘TLS’ to specify the minimum TLS protocol version to be used for ‘https://’ URLs (_inter alia_ providing a means to check for sites using deprecated TLS versions 1.0 and 1.1).
‘capture.output()’ no longer uses non-standard evaluation to evaluate its arguments. This makes evaluation of functions like ‘parent.frame()’ more consistent, thanks to Lionel Henry's PR#17907.