Is repeating words in mind necessary to some meditations in Theravada? Why or why not?

According to Visuddhimagga, focusing on breath does't require repeating "inhalation, exhalation..." in mind (at least it seems that the book doesn't explicitly tell that) . However, the 10 Kasinas and the 10 foulness may need repetitive words in mind. For example: > "Anyone else should use that same kind of circle of luminosity just described, developing it as “luminosity, luminosity” or “light, light.”(Vm. The Remaining Kasinas.The Light Kasina) I think that the principle of the 10 Kasinas is focusing on concepts of meaning. So maybe repeating the concepts of word isn't necessary. Many modern experts also imply repeating words when meditating but give no further explanation.