This includes issuing principles-based guidance, which sometimes includes "best practices" that institutions should adopt in following the recommendations contained in the guidance. Principles-based guidance can often be a more flexible tool than rules for accomplishing regulators' goals. This flexibility allows supervisory agencies to adapt the guidance to different situations.
One reason is that the regulators’ definition of liquidity is highly concentrated on government bonds. As the current environment shows, some market segments of government bonds can eventually dry up. Another reason is the respective definitions of the Net Stable Funding Ratio (NSFR) and the Liquidity Coverage Ratio (LCR). –  The LCR is the main component of Basel III’s liquidity regime.