I heard this just now; Non Regional Diction. It was in the context of a woman trying to break into the man's world of TV news in the 70's. It was something she had to practice.
It reminded me of a memory, and a story.
When I ws growing up, the dominant foreign culture around me was British. Of the people my family socialized with, the accent I heard most was English. I enjoyed Monty Python, and The Goodies and others. I could immitate it well.
Where I lived, I used to hear other accents on TV or in movies and think... how is it possible that I live where nobody has accent. How is it that everyone else did, but my town was "normal".
I used Television and the dictionary as my guide. I sounded like the people on TV, except of course when the TV character had an accent, but that goes without saying. I could identify Boston, New York, Southern, Texan, Carebean and English accents. I could recognise Spanish and French and Russion accents, but when I talked, I sounded accent-less. The way the dictionary meant the words to sound.
I never understood it when Americans told me Canadians said "Aboot" because I always said About. I said it like the TV.
Today, at 43 I understand a little more. I do have an accent on some words, but I grew up with more TV than any other verbal influence, and for the most part, TV has developed a non-regional dialect.
Things that go without saying, should be said more often.