flags: define "implicit"

[matttbe]

Mainly to add a comment about that: it cannot be set from the userspace, so it should not be used in path-managers.

Suggested-by: @sskras

[coveralls]

Pull Request Test Coverage Report for Build 19679730433

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 67.044%

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Totals
Change from base Build 19644312326:	0.0%
Covered Lines:	1481
Relevant Lines:	2209

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💛 - Coveralls