@java.lang.Override
  protected com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
      internalGetFieldAccessorTable() {
    return com.google.devtools.cloudtrace.v2.TraceProto
        .internal_static_google_devtools_cloudtrace_v2_Span_fieldAccessorTable
        .ensureFieldAccessorsInitialized(
            com.google.devtools.cloudtrace.v2.Span.class,
            com.google.devtools.cloudtrace.v2.Span.Builder.class);
  }
<pre>
A span represents a single operation within a trace. Spans can be
nested to form a trace tree. Often, a trace contains a root span
that describes the end-to-end latency, and one or more subspans for
its sub-operations.

A trace can also contain multiple root spans, or none at all.
Spans do not need to be contiguous. There might be
gaps or overlaps between spans in a trace.
</pre>

Protobuf type {@code google.devtools.cloudtrace.v2.Span}
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/Span.java