CASELAW-EPO - reviews of EPO Boards of Appeal decisions

T 821/20 -  No systematic recourse to the description when interpreting claims – Added subject-matter

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The patent relates to safety triple glazing for building facades.

Brief outline of the case

The opponent appealed the OD’s decision of maintenance according to AR1.

The subject matter of claim 1 as upheld by the OD is essentially based on the combination of claims 1, 2, 4 and 9 as filed, with a further amendment reading:  “Triple glazing … at least one sheet of which is a laminated assemblythe laminated assembly being positioned so as to …, this assembly comprising two systems of infrared-reflecting thin layers, on the faces at position 2 and 5, or at position 3 and 5, the faces being numbered starting from the one turned towards the exterior.

The board held that the feature “the assembly” did not find any support in the application as filed and hence the claim as maintained infringed the requirements of Art 123(2).

The patent was revoked.

The OD’s position

According to the OD, the numbering of the positions is conventionally used to define the surfaces of a multi-layered pane, 1 being the outermost surface, 2 the inner surface of the first pane, 3 the outer surface of the second pane, and so on. The person skilled in the art would therefore easily recognise that the said numbering could only concern the faces of the triple glazing and not the faces of the laminated assembly.

The proprietor’s position

The proprietor accepted that there was an ambiguity in the wording of the claim, but argued that it should be resolved by interpretation in the light of the description as filed, which made it clear and referred to page 3, line 13; subparagraph straddling pages 6 and 7 and 1st subparagraph on page 7. The proprietor considered that the expression “this assembly” should be interpreted as “the glazing“.

The board’s position

For the board, the term “assembly” is defined in the first part of the claim as referring tothe laminated assembly“, so that the subsequent phrase “this assembly comprising two systems of thin layers...” represents a clear and direct indication that these thin layers are part of the laminated assembly and therefore the numbering of their positions refers to the surfaces of the laminated assembly and not those of the triple glazing.

The board did thus not agree with the proprietor. The board held that the wording of claim 1 clearly defines the infra-red reflecting thin films as part of “said assembly”, which refers to the laminated assembly previously defined in the claim, thus implying that the numbering relates to the faces of the laminated assembly and not those of the triple glazing.

Reference to the description in order to interpret the claims

Contrary to the proprietor’s view, the board held that in the present case it is neither necessary nor justified to interpret the claim in the light of the description.

In this respect the Board cited T 169/20 (points 1.4.3 and 1.5) and T 1127/16, point 2.6. 1), which held that where the claim language is clear and technically reasonable in the underlying technical context, there is no justification for relying on the description to restrict the scope of the claim by excluding interpretations which are both reasonable and technically sensible in the technical context of the patent.

For the board it would be tantamount to rewarding ambiguous claim drafting by allowing the proprietor to rely on the description to narrow the claim’s subject matter to his or her liking rather than clarifying the claim’s subject matter.


The decision is interesting in that it confirms the recent decision T 169/20 as well as T 1127/16.

In T 1127/16 the board held that the fact that a claim of a patent is to be construed by a mind willing to understand and not a mind desirous of misunderstanding, does not mean that the description and the drawings have automatically to be consulted when an “ambiguous” feature (i.e. a feature which at least theoretically allows more than one interpretation) occurs in the claim, or where the claim as a whole includes one or more inconsistencies, to resolve that ambiguity or inconsistency. Rather, the claim should essentially be read and interpreted on its own merits.

In T 821/20, the problem is about added subject-matter, in T 169/20 it was about clarity as such.

The present decision shows once more that a referral to the EBA in order to clarify the situation whether or not the description is to be taken into account when interpreting claims is highly necessary.

Whether the question of the adaptation of the description to the claims should also be discussed during this referral remains open. A decision on the interpretation of the claims with or without recourse to the description could indirectly give an answer to the question of the adaptation of the description to the claims.


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