Final answer:
HR metrics primarily operate within the domain of descriptive analytics, which involves interpreting historical data to understand the current state of the workforce and extrapolate patterns and trends.
Step-by-step explanation:
The initial workforce analytic domain within which HR metrics functions largely is descriptive analytics. This domain involves the use of data to understand and benchmark the current state of the workforce. Descriptive analytics provides insights into what has happened within an organization by interpreting historical data. It allows HR professionals to create reports on metrics such as turnover rates, employee satisfaction, and average training costs. By analyzing this data, organizations can see patterns and trends, which can help in future decision-making processes and planning.