I am trying to make a file to add support for syntax highlighting for Axe code in vim, and in the list of tokens I'd like to support is for example "[|a] [|b]".
However, when I try to open an "Axe file" with this syntax file, it says an error (can't tell exactly which error, I have two PCs, one with internet (this one) and the other one without (the one I am experiencing issues with vim)) about "a]" and "[", as if every "|" character broke the line or something and then what it saw was "[" followed with "a]" followed with "[".

So any idea what this character does ?
And most of all, any idea how I could get vim to highlight "[|a]" without getting an error when opening my files ?