Plain vowels are just what you imagine. There are seven of them in the alphabet:
α, ε, η, ι, ο, υ, ω, and their stressed versions are: ά, έ, ή, ί, ό, ύ, ώ.
Not much to mention here, except that when words are written in CAPITALS, the stress is not marked.
But there is a case where capital letters can get an accent mark in writing: it is when the capitalized first letter of a phrase which is otherwise in lowercase, is stressed.
The capital vowels with stress look like this: Ά, Έ, Ή, Ί, Ό, Ύ, Ώ
However reading this on the browser, the capital vowels with stress look like this: Α, Ε, Η, Ι, Ο, Υ, Ω
It would be nice to see it correctly in the browser too!
Example: Όμηρος i.e. Homer becomes Ομηρος
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