Final answer:
The diction of the excerpt from The Youngest Doll is casual and informal.
Step-by-step explanation:
The diction of the excerpt from The Youngest Doll can best be described as casual and informal. The passage does not use lofty or archaic language, nor does it contain vivid and figurative language. Instead, the diction is simple and conversational, using everyday words and phrases. An example of this is the use of the phrase 'they seemed to swoon together at the very borderland of life's mystery.'