What are the rules for "w" word motion when characters are not in iskeyword?

Question

If I have a shell script with code like

...
chars+=('5')
chars+=('6')
...
chars+=('%')
chars+=('&')
...

and iskeyword is defined as

iskeyword=@,48-57,_,192-255,-

This definition indicates to me Vim will consider a continuous sequence of characters from these iskeywords characters to be a word.
So if I am here

chars+=('5')
 ^ (cursor)
chars+=('6') 

and press w

chars+=('5')
     ^ (cursor)
chars+=('6')

I end up on + which is not the beginning of a word as defined by iskeyword character set. Why? Does Vim stop at the beginning of a group of these non-iskeyword chars because it considers you might be interested in doing something with them?

In this case, wouldn't it be better to say w takes you both to the beginning of the next "word" OR the beginning of the next "anti-word" (continuous sequence of characters NOT defined in iskeyword)?

Because code contains a lot of characters not in iskeyword, I am interested in knowing the rules for "w" word motion regarding these non-word characters.

Answer 1

I think the misunderstanding is that iskeyword doesn't define what a word is; rather, it adjusts where a boundary may happen by adjusting what a keyword is. Both keywords and non-keywords are still "words".

According to :help word:

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.

But, that doesn't quite answer your question exactly.

My understanding is that "iskeyword" is used to group the containing characters as a type of word called "keyword", but that doesn't mean that characters (except whitespace) outside of iskeyword aren't words, but are just non-keywords. Also, it seems that letters and high unicode is considered part of a keyword regardless (from help 'iskeyword' and help 'isfname').

As such, when you press w at the beginning of chars+=, the letters are considered part of the same word because they form a keyword, but since + and = are not in iskeyword, that makes them a non-keyword word, which means there is a word separation.

The behavior that I observe is that, outside of whitespace separation, keywords and non-keywords are considered words, and a transition from keyword to non-keyword or from non-keyword to keyword forms a word boundary, just like whitespace forms a word or WORD boundary.