It is a well-established principle of claim construction that it is not permissible to vary or qualify the plain and unambiguous meaning of the claim by reference to the body of the specification. Frequently however, it will be necessary to look beyond the words of a claim in order to give proper context to the language employed. Two recent decisions of the Full Federal Court provide important guidance on how functional requirements can impact on claim construction and the role of expert evidence in that process.

In Artcraft v Streetworx1, the court was required to construe the term ‘visible’ in the context of a street lighting assembly. Specifically, the claim in question required that the lighting assembly have a visor which covered an internal compartment, referred to as the ‘termination chamber’, with at least part of that chamber ‘being visible through the visor’.

As noted by the trial judge, the claim itself did not provide any express content or context to the term ’visible’, leaving open the question ‘How clearly visible is a part of the termination chamber to be?’.

The key to construing the term lay in the patent’s description of one embodiment of the invention, stating that:

Preferably, the components located within the “termination chamber” … are visible through the visor. For example, this part of the visor may be clear or lightly frosted compared to the remainder of the visor.

… a preferred embodiment of the present invention allows a linesman to carry out a visual inspection of the components without having to remove any covers.’

Agreeing with the construction put forward by the patentee, the trial judge found that the term ‘visible’, as used in the claim, meant that one could see the presence of components located

within the ‘termination chamber’ through the visor, but not necessarily the components in detail.

On appeal, Artcraft contended that the trial judge had erred in separating the described preference for the components located within the ‘termination chamber’ being visible through the visor from the associated advantage of allowing a linesman to carry out a visual inspection of the components without having to remove any covers.

The majority of the Full Court was not satisfied that the trial judge had made such an error and rejected the appeal. Although the specification itself did not establish any clear functionality for a level of visibility which fell short of allowing inspection of the internal components, there was expert evidence that there might be some practical benefit, such as allowing assessment of whether insects or spiders were contaminating the chamber.

In a dissenting judgement, Jessup J concluded that having regard to the specification as a whole, the term ‘visible’ was linked to, and given context by, the functional requirement of allowing inspection of the components within the ‘termination chamber’. While a skilled reader might appreciate that there could be other advantages associated with a lower degree of visibility, the specification was not drafted with those advantages in mind. Such considerations would therefore not influence the skilled reader’s understanding of the term ’visible’ as used in the claim.

Jessup J also commented on the patentee’s submissions that it was not legitimate, in the absence of an express reference, to import features of a preferred embodiment into a claim to limit its scope. The cases establishing that proposition were said not to qualify the conventional rule that recourse may be had to any clearly relevant part of the specification for the purpose of understanding the character of the invention to which a claim relates or of resolving terms of the claim which may be ambiguous. Where the claim language itself derives from the description of a preferred embodiment, any recourse to the specification for constructional purposes in relation to the claim would of necessity be to the passage in which that embodiment is described. As such, in appropriate circumstances, it is permissible to construe a claim by reference to functional requirements attributable to a preferred embodiment.

In Multigate v Braun2, the court was required  to construe the term ‘spaced apart’ used in the context of a medical device. From the outset, the court noted that the evidence of a skilled reader is not determinative of a construction question.   It is always a matter for the Court to construe the particular claim adopting the relevant lens, but giving such weight to the expert evidence that it sees fit. If words or phrases are used in a claim  in their ordinary English meaning, their meaning cannot be distorted by an expert’s use of a functionality lens to give them an application in tension with their plain meaning.

At first instance, it was held that the expression ’spaced apart’ did not require there to be a gap between the two relevant parts, and that they could be in a ‘spaced apart relationship’, even though they might be touching, provided that they were not constructed so as to be connected. This conclusion was in part based on expert evidence as to the functional requirements of the relevant components.

The trial judge noted that any space or gap between the two parts would serve no function. What did serve a function was that the two be separate for the operation of the device. The relationship of being ‘spaced apart’ was not a relationship which prevented the two from having a connection or touching at all times. Rather, a gap between the two only became a necessary feature in the operation of the device and was provided for by a construction which ensures that a gap emerges during operation.

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The Full Court rejected this conclusion, stating that the trial judge’s approach was erroneously influenced by irrelevant functional considerations. In their view, such a construction had the effect  of varying or qualifying a clear and unambiguous term in the claim. While there was expert evidence that physical separation of the components was not functionally necessary, there was nothing to suggest that the words ’spaced apart’ had any special technical meaning. There was no reason why the words should be given anything other than their ordinary English meaning. That meaning did not encompass a situation in which there was no gap between the relevant parts.

From these decisions, it is apparent that functional considerations can provide important context in which a claim is construed. However, the primary source of such context is the specification itself. Functional considerations which are not linked to the claim language via the specification, or which are contrary to the plain meaning of that language, may be of limited assistance.

If the words used in a claim are intended to have a particular meaning which might differ from their plain everyday meaning or are intended to import a functional requirement associated with how the invention works in practice, then it is crucial that such a meaning or function is adequately described in the specification.