Require tracer to add ignored parents as links

specification/api-tracing.md

@@ -288,6 +288,14 @@ a root span, and MUST generate a new `TraceId` for each root span created.
 For a Span with a parent, the `TraceId` MUST be the same as the parent.
 Also, the child span MUST inherit all `TraceState` values of its parent by default.
 
+If the implementation chooses to ignore possible parent in `Context` (because an
+option to create a root span was used), then the implementation SHOULD add those
+possible parents as [`Link`s](#add-links) to the new `Span` with an
+[attribute](#set-attributes) denoting whether the ignored parent was a current
+`Span` or an extracted `SpanContext`. The attribute MUST have a key
+`ignored-parent`, and value `local` and `remote` for ignored current `Span` and
+extracted `SpanContext`, respectively.
+
 A `Span` is said to have a _remote parent_ if it is the child of a `Span`
 created in another process. Each propagators' deserialization must set
 `IsRemote` to true on a parent `SpanContext` so `Span` creation knows if the