I got more details after trying:
foo.core$macros=> (defmacro $ [tag props & children]
#_=> `(let [props# ~props
#_=> attrs# (respo.util.list/pick-attrs props#)
#_=> styles# (if (contains? props# :style) (sort-by first (:style props#)) (list))
#_=> event# (or (:on props#) (:event props#) {})
#_=> child-map# (respo.util.list/arrange-children-old ~children)]
#_=> {:name ~tag,
#_=> :coord nil,
#_=> :attrs attrs#,
#_=> :style styles#,
#_=> :event event#,
#_=> :children child-map#}))
#'foo.core$macros/$
foo.core$macros=> (macroexpand '(foo.core/$ :div {} []))
(let*
[props__41__auto__
{}
attrs__42__auto__
(respo.util.list/pick-attrs props__41__auto__)
styles__43__auto__
(if
(cljs.core/contains? props__41__auto__ :style)
(cljs.core/sort-by cljs.core/first (:style props__41__auto__))
(cljs.core/list))
event__44__auto__
(cljs.core/or (:on props__41__auto__) (:event props__41__auto__) {})
child-map__45__auto__
(respo.util.list/arrange-children-old ([]))]
{:name :div,
:coord nil,
:attrs attrs__42__auto__,
:style styles__43__auto__,
:event event__44__auto__,
:children child-map__45__auto__})