Framework
PCI DSS v4.0: what it asks of a production change
Requirement 6 of PCI DSS v4.0 covers bespoke software review (6.2.3) and change control in production (6.5.1 to 6.5.4). It applies to the systems in the cardholder data environment; name them in the preamble and PCI DSS clauses show on those rows only.
Summarised: a one-line statement of what the requirement asks. The standard's own text is not held in full here, so it is not quoted.