Why a Definition of Done exists
Without a shared Definition of Done, "done" quietly means something different to every person on the team: one developer's done is code merged, another's is code merged and tested, and a story can bounce between "finished" and "not actually finished" for days because nobody agreed on the bar in advance. A written Definition of Done removes that ambiguity before the argument happens, not after.
Using the checklist
The default items cover the common ground most teams need (code review, tests, no regressions, documentation, deployment, demoability), but every team's real Definition of Done includes things specific to their stack and process. Uncheck what doesn't apply, and add what does: a specific accessibility check, a particular team's sign-off, a performance budget the team actually enforces.
Definition of Done vs. acceptance criteria
These answer different questions and both matter: acceptance criteria describe what makes this specific story correct; Definition of Done describes the quality bar every story has to clear regardless of what it is. A story can meet all its acceptance criteria and still not be Done if the team's Definition of Done (tests, review, documentation) hasn't been satisfied.
