Does Modern Standard Arabic ever overlap with colloquial Arabic?
They certainly do, as a mater of fact it is very difficult to find a situation where one type is used exclusively. For example, MSA is used in formal speeches or interviews. However, just as soon as the speaker diverts away from his well-prepared speech in order to add a comment or respond to a question, the rate of colloquial usage in this speech increases dramatically. How much MSA versus colloquial is used depends on the speaker, the topic, the situation – amongst other factors. At the other end of the spectrum, public education as well as exposure to mass media, has introduced MSA elements amongst the least educated so that it would be equally difficult to find an Arab speaker whose speech is totally unaffected by MSA.