Use of "World" in invocatory verse

[George Hart]

It is customary to use the word "ulakam" -- "world" (probably from Skt. loka) -- in invocatory verses (kaṭavuḷ vāḻttu) in Tamil.  "World" is also found in some invocations in Sanskrit (e.g. the first verse of the Raghuvaṃśa -- jagataḥ pitarau).  Does anyone know of any articles on this custom?  I have a student who needs to research it further.  (It's worth noting also that the RV has what is called "avai aṭakkam" in Tamil, in which the poet says in the most poetic possible language what a worthless poet he is, something also found commonly in Tamil). -- Thanks -- George Hart