y a w twitches around the word, which means that there is a space after the word, it will also capture it (but not the space before).
y i w is yank inside the word, which occupies only the characters of the word.
You can see that v a w or v i w will shake to select the same characters. Then you can press y to execute yank.
i and a , of course, apply to all other VIM groups, such as W , which is any non-decomposition.
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