Classes for performing table joins by matching rows to each other. The matching is done in an entirely configurable and pluggable way by defining a {@link uk.ac.starlink.table.join.MatchEngine} which defines what counts as a match between two tuples (rows) and can be used to work out what counts as a near miss too. Matching is (except in pathological cases) an O(N ln N) process, where N is the total number of rows in all the tables participating in a match. `MatchEngine` implementations are provided for a number of (astronomically) common cases, including N-dimensional Cartesian, spherical polar, exact value and Sky matching (the Sky one uses the HEALPix scheme). You can also combine matches to an arbitrary level of complexity.