* This method is from opentracing-java. {@see https://github.com/opentracing/opentracing-java/blob/release-0.20.9/opentracing-api/src/main/java/io/opentracing/Span.java#L91}
* <p>
* Log key:value pairs to the Span with the current walltime timestamp.
* <p>
* <p><strong>CAUTIONARY NOTE:</strong> not all Tracer implementations support key:value log fields end-to-end.
* Caveat emptor.
* <p>
* <p>A contrived example (using Guava, which is not required):
* <p> Log key:value pairs to the Span with the current walltime timestamp. <p> <p><strong>CAUTIONARY NOTE:</strong>
* not all Tracer implementations support key:value log fields end-to-end. Caveat emptor. <p> <p>A contrived example
* This method is from opentracing-java. {@see https://github.com/opentracing/opentracing-java/blob/release-0.20.9/opentracing-api/src/main/java/io/opentracing/Span.java#L120}
* <p>
* Record an event at the current walltime timestamp.
* <p>
* Shorthand for
* <p>
* <p> Record an event at the current walltime timestamp. <p> Shorthand for <p>