Assertion: 'For the purposes of applying the bidirectional algorithm to the paragraph-level container that a bdi element finds itself within, the bdi element must be treated like a U+FFFC OBJECT REPLACEMENT CHARACTER.' Thus, regardless of its content and its dir attribute (if any), a BDI will not prevent a strongly RTL (or LTR) character preceding it from forming a single directional run with another strongly RTL (LTR) character following it.