What does the exclamation HEEEEE mean?

Reference 1, Most commonly used for an exclamation directed to someone who is having some sort of accident, usually used in the funny context, for example; Your friend trips over in a clumsy and harmless manner and you could point at them laughing and say, HEEEEE, how CLUMSY of you.

Reference 2; May also be used as an expression of guiltiness or embarrasment, for example; your friend who clumsily tripped over could get up sheepishly and say Heeee, sort of laughing at themselves.

Reference 3: May also be rarely used to acknowledge something, for example: Someone shows you something interesting in a book etc and you response may be "heee".

HEEEEE, in the main form may also be cut down or used for short in the context of EEEEEEEEE or even shorter e e e e.