Both of these are really the same skill: designing the rule rather than the instance.

• A component library is not a design system. The system is the decisions — spacing scale, type scale, colour roles, interaction patterns — and the library is one expression of them.
• Tokens are the contract between design and engineering. Named semantically (surface, danger, muted) rather than literally (grey-100), so a theme change does not require renaming everything.
• The hard part is adoption, exactly as with an internal platform. A system product teams route around is a museum. Contribution paths and genuine responsiveness to requests are what prevent that.
• Version and deprecate deliberately, or you accumulate three button components and nobody knows which is current.

• It is a design constraint, not an audit. Retrofitting contrast and focus order at the end is expensive and produces worse design than accounting for them at the start.
• The four that catch most issues: contrast ratios, keyboard operability with visible focus, meaningful labels and alternative text, and not using colour alone to convey meaning.
• Motion and reduced-motion preferences, which are routinely forgotten and genuinely affect people.
• It is increasingly a legal requirement, not only an ethical one, which is part of why 51% of postings name it.