  In a locally $\lambda$-presentable category, with $\lambda$ a regular
cardinal, classes of objects that are injective with respect to a family of
morphisms whose domains and codomains are $\lambda$-presentable, are known to
be characterized by their closure under products, $\lambda$-directed colimits
and $\lambda$-pure subobjects. Replacing the strict commutativity of diagrams
by "commutativity up to $\varepsilon$", this paper provides an "approximate
version" of this characterization for categories enriched over metric spaces.
It entails a detailed discussion of the needed $\varepsilon$-generalizations of
the notion of $\lambda$-purity. The categorical theory is being applied to the
locally $\aleph_1$-presentable category of Banach spaces and their linear
operators of norm at most 1, culminating in a largely categorical proof for the
existence of the so-called Gurarii Banach space.
