erlang - pub/sub with gproc - what is module? -

reading gproc docs, looks key used routed messages different processes, can't figure out how pub/sub example works in docs, seems using different keys registering , sending messages.

in gproc docs, provide following example of implementing pub/sub:

subscribe(event) ->     gproc:reg({p, l, {?module, event}}).  publish(event, data) ->     gproc:send({p, l, {?module, event}}, {?module, event, data}). 

the gproc:send 2nd argument: {?module, event, data}, wouldn't make message different based on module sending event?

so example if subscribe event of type foo_bar module1:

pub_sub:subscribe(foo_bar). 

and publish event module2:

pub_sub:publish(foo_bar, {color, "blue"}). 

the calls gproc first call be:

gproc:reg({p, l, {module1, foo_bar}}). 

while second:

gproc:send({p, l, {module2, foo_bar}}, {module2, foo_bar, {color, "blue}}). 

so seems keys different: {p, l, {module1, foo_bar}} , {p, l, {module2, foo_bar}}, , module1 never receive message.

or missing something?

p.s.: there different syntax here, still see same problem:

subscribe(eventtype) ->     %% gproc notation: {p, l, name} means {(p)roperty, (l)ocal, name}     gproc:reg({p, l, {?module, eventtype}}).  notify(eventtype, msg) ->     key = {?module, eventtype},     gproc:send({p, l, key}, {self(), key, msg}). 

nevermind. key same, because ?module macro expands module defined in!

so {p, l, {pub_sub, foo_bar}} both calls.

references: this post useful in understanding gproc.