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ESTOPPEL DOCTRINE MAY APPLY IN TRADEMARK DIS-PUTES
"Prosecution history estoppel" (PHE, also known as "file wrapper estoppel") is an important legal doctrine in patent infringement litigation and other patent-related disputes. The Patent Act does not make any provision with regard to es-toppel, but the Patent Infringement Assessment Guidelines drawn up by the Intellectual Property Office state that PHE prevents a patentee from relying on the "doctrine of equivalents" to reas-sert content that has been narrowed or abandoned at any time or in any document, from the appli-cation filing stage to the patent maintenance stage.
Patent claims are the basis for deciding the scope of patent rights, and once a granted patent has been published, any person may obtain docu-ments from any stage of the patenting process, from filing to maintenance. The Guidelines state that based on the principle that others should be able to rely upon all amendments, corrections, responses, and defenses made by the patentee throughout that process, the patentee may not use the doctrine of equivalents to reassert content previously restricted or excluded.
The Trademark Act and other legislation have no express provision as to whether the doctrine of PHE can apply to trademark infringement cases or other trademark disputes. Therefore, although in many past cases parties have asserted the PHE doctrine, the courts have rarely expressed spe-cific opinions on this issue.
However, in a number of recent judgments, the Supreme Administrative Court has expressed the view that it is possible for the doctrine of PHE to apply in trademark disputes. For example, in a 2005 judgment in an appeal arising out of a trademark opposition, the Supreme Administra-tive Court stated that the doctrine of estoppel may be applied only when there is clearly no disagreement regarding physical evidence or specific assertions. In that case, far from con-ceding that the opposed mark was not similar to the prior-registered mark on which the opposi-tion was based, the opposition petitioner had expressed no opinion as to whether the two marks were similar. Therefore the doctrine of estoppel was not applicable to that case.