Vim: word vs WORD

Question

I'm learning Vim and can't wrap my head around the difference between word and WORD.

I got the following from the Vim manual.

A word consists of a sequence of letters, digits and underscores, or a sequence of other non-blank characters, separated with white space (spaces, tabs, ). This can be changed with the 'iskeyword' option. An empty line is also considered to be a word.

A WORD consists of a sequence of non-blank characters, separated with white space. An empty line is also considered to be a WORD.

I feel word and WORD are just the same thing. They are both a sequence of non-blank chars separated with white spaces. An empty line can be considered as both word and WORD.

Question:
What's the difference between them?
And why/when would someone use WORD over word?

I've already done Google and SO search, but their search-engine interpret WORD as just word so it's like I'm searching for Vim word vs word and of course won't find anything useful.

Answer 1

• A WORD is always delimited by whitespace.
• A word is delimited by non-keyword characters, which are configurable. Whitespace characters aren't keywords, and usually other characters (like ()[],-) aren't, neither. Therefore, a word usually is smaller than a WORD; the word-navigation is more fine-grained.

Example

This "stuff" is not-so difficult! wwww  wwwww  ww www ww wwwwwwwww    " (key)words, delimiters are non-keywords: "-! and whitespace WWWW WWWWWWW WW WWWWWW WWWWWWWWWW   " WORDS, delimiters are whitespace only 

Answer 2

To supplement the previous answers... I visualise it like this; WORD is bigger than word, it encompasses more...