CLHS: Section 7.6.5.1

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## 7.6.5.1 Examples of Keyword Arguments in Generic Functions and Methods

For example, suppose there are two methods defined for `width` as follows:

     (defmethod width ((c character-class) &key font) ...)

     (defmethod width ((p picture-class) &key pixel-size) ...)

Assume that there are no other methods and no generic function definition for `width`. The evaluation of the following form should signal an error because the keyword argument `:pixel-size` is not accepted by the applicable method.

     (width (make-instance `character-class :char #\Q)
            :font 'baskerville :pixel-size 10)

The evaluation of the following form should signal an error.

     (width (make-instance `picture-class :glyph (glyph #\Q))
            :font 'baskerville :pixel-size 10)

The evaluation of the following form will not signal an error if the class named `character-picture-class` is a subclass of both `picture-class` and `character-class`.

     (width (make-instance `character-picture-class :char #\Q)
            :font 'baskerville :pixel-size 10)

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