diff --git a/pep-0517.txt b/pep-0517.txt index 295c55c0f..1ad562030 100644 --- a/pep-0517.txt +++ b/pep-0517.txt @@ -374,9 +374,11 @@ dictionary provided as an "escape hatch" for users to pass ad-hoc configuration into individual package builds. Build backends MAY assign any semantics they like to this dictionary. Build frontends SHOULD provide some mechanism for users to specify arbitrary -string-key/string-value pairs to be placed in this dictionary. For -example, they might support some syntax like ``--package-config -CC=gcc``. Build frontends MAY also provide arbitrary other mechanisms +string-key/string-value pairs to be placed in this dictionary. +For example, they might support some syntax like ``--package-config CC=gcc``. +In case a user provides duplicate string-keys, build frontends SHOULD +combine the corresponding string-values into a list of strings. +Build frontends MAY also provide arbitrary other mechanisms for users to place entries in this dictionary. For example, ``pip`` might choose to map a mix of modern and legacy command line arguments like::