  Many project-specific languages, including in particular filtering languages,
are defined using non-formal specifications written in natural languages. This
leads to ambiguities and errors in the specification of those languages. This
paper reports on an industrial experiment on using a tool-supported language
specification framework (K) for the formal specification of the syntax and
semantics of a filtering language having a complexity similar to those of
real-life projects. This experimentation aims at estimating, in a specific
industrial setting, the difficulty and benefits of formally specifying a packet
filtering language using a tool-supported formal approach.
