What's the difference between require and require-dev? [duplicate]

Answer 1

seems clear to me:

require

Lists packages required by this package. The package will not be installed unless those requirements can be met.

require-dev (root-only)

Lists packages required for developing this package ⁽¹⁾, or running tests, etc. The dev requirements of the root package only will be installed if install is run with --dev or if update is run without --no-dev.

http://getcomposer.org/doc/04-schema.md

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1. the packages used to develop a package