Perhaps it would be better to change it to
`/\A([#\\]|[^#\\]*([#\\][^\\#\{][^#\\]*)*)/`
not to favor `#` more than `\`.
And changing it to
`/\A([#\\]?[^#\\]*([#\\][^\\#\{][^#\\]*)*)/`
actually takes care of the leading `#` or `\` as well - I'll commit that.