What is Risk-based attribution?

Risk-based attribution explains the day’s P&L by a Taylor expansion in the risk-factor moves, using the start-of-day Greeks: $\Delta V\approx\delta\,\Delta f+\tfrac12\Gamma\,\Delta f^2+\nu\,\Delta\sigma+\tfrac12\,\mathrm{volga}\,\Delta\sigma^2+\mathrm{vanna}\,\Delta f\,\Delta\sigma+\theta\,\Delta t$.