套件：php-psr-log（1.1.4-2）
common interface for logging libraries
The main goal is to allow libraries to receive a Psr\Log\LoggerInterface object and write logs to it in a simple and universal way. Frameworks and CMSs that have custom needs MAY extend the interface for their own purpose, but SHOULD remain compatible with this document. This ensures that the third-party libraries an application uses can write to the centralized application logs.
The LoggerInterface exposes eight methods to write logs to the eight RFC 5424 levels (debug, info, notice, warning, error, critical, alert, emergency).
A ninth method, log, accepts a log level as first argument. Calling this method with one of the log level constants MUST have the same result as calling the level-specific method. Calling this method with a level not defined by this specification MUST throw a Psr\Log\InvalidArgumentException if the implementation does not know about the level. Users SHOULD NOT use a custom level without knowing for sure the current implementation supports it.
Note that this is not a logger of its own. It is merely an interface that describes a logger. See the specification for more details.