Why does pressing < c-i > trigger < c-y > when < tab > is < c-y >?

  question, vim

In the insert mode,<c-j>And<cr>The same is true of. But mapping<cr>For<Esc>When, press<c-j>When, will not enter the normal mode.
Feeling<c-i>And<tab>The relationship is similar to the former, but the performance is different. I use<tab>MappingemmetThe<c-y>, but<c-i>It will also trigger<c-y>. I.e. using non-recursive mappinginoremapThe same is true.

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Please learn to use: help [key position] to see their essence, for example:help i_CTRL-JHere’s the thing:

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Another example is:help i_CTRL_IHere’s the thing:

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I think the help document is already very telling.