Practice and ideas of ‘high’ and ‘low’

1. Does "in both cases" mean "in both art and advertisement"?

2. Does "practice and ideas of ‘high’ and ‘low’" mean {practice and ideas} of {high and low}, that is high and low practices and ideas?

3. What is it that will be returned to throughout this book? "the fluidity of practices, forms, themes and ideas"?

Context:

One of these possibilities is the synthesis of the verbal and the visual that, as I have shown, has occurred in different ways in art and advertising but which, in both cases, has also resulted in a synthesis of art and advertising. This synthesis is symptomatic of the way that the boundaries between arenas of practice and ideas of ‘high’ and ‘low’ are collapsing in the culture as a whole and provides a fitting introduction to the fluidity of practices, forms, themes and ideas that will be returned to throughout this book.