Map from reader tag symbols to data reader Vars. When Clojure starts, it searches for files named 'data_readers.clj' and 'data_readers.cljc' at the root of the classpath. Each such file must contain a literal map of symbols, like this: {foo/bar my.project.foo/bar foo/baz my.project/baz} The first symbol in each pair is a tag that will be recognized by the Clojure reader. The second symbol in the pair is the fully-qualified name of a Var which will be invoked by the reader to parse the form following the tag. For example, given the data_readers.clj file above, the Clojure reader would parse this form: #foo/bar [1 2 3] by invoking the Var #'my.project.foo/bar on the vector [1 2 3]. The data reader function is invoked on the form AFTER it has been read as a normal Clojure data structure by the reader. Reader tags without namespace qualifiers are reserved for Clojure. Default reader tags are defined in clojure.core/default-data-readers but may be overridden in data_readers.clj, data_readers.cljc, or by rebinding this Var.