句子请教

zipee

王若平－难句分析－分割结构－第65页中：第44句：
if its message were confined merely to information -- and that in itself would be difficult if not impossible to achieve,for even a detail such as the choice of the colour of a shirt is subtly persuasive -- advertising would be so boring that no one would pay any attention.

其中：\"-- and that in itself\"中的:
1:and是什么结构？是并列吗？并列什么？或是递进？
2:that指代什么？是前面\"if its message were confined merely to information\"整句话么？