Variables
Const B3_CONTEXT_HEADER
B3_CONTEXT_HEADER: "b3" = 'b3'
Const X_B3_FLAGS
X_B3_FLAGS: "x-b3-flags" = 'x-b3-flags'
Const X_B3_PARENT_SPAN_ID
X_B3_PARENT_SPAN_ID: "x-b3-parentspanid" = 'x-b3-parentspanid'
Const X_B3_SAMPLED
X_B3_SAMPLED: "x-b3-sampled" = 'x-b3-sampled'
Const X_B3_SPAN_ID
X_B3_SPAN_ID: "x-b3-spanid" = 'x-b3-spanid'
Const X_B3_TRACE_ID
X_B3_TRACE_ID: "x-b3-traceid" = 'x-b3-traceid'
B3 single-header key