A zenoh resource is represented by a pair composed by a key and a
value, such as, (/car/telemetry/speed, 320). A resource key
is an arbitrary array of characters, with the exclusion of the symbols
*, **, ?, [, ], and #,
which have special meaning in the context of zenoh.
A key including any number of the wildcard symbols, * and **,
such as, /car/telemetry/*, is called a key expression as it
denotes a set of keys. The wildcard character * expands to an
arbitrary string not including zenoh’s reserved characters and the /
character, while the ** expands to strings that may also include the
/ character.
Finally, it is worth mentioning that for time and space efficiency matters,
zenoh will automatically map key expressions to small integers. The mapping is automatic,
but it can be triggered excplicily by with zenoh::Session::declare_keyexpr().