Suggestion: Allow default scss/dollar-variable-pattern to match variables like $x1

[kerryj89]

My sass math functions had variables like $x1 and $y1, so I updated the pattern to be: ^[a-z][0-9]?(-*[a-z0-9]+)*$. Is there some sass convention that says variables can't be one letter or a letter paired with a number that you often see in loops or math?

[bjankord]

I'm open to updating this.