'local' is a reserved word in zsh 5.1 but not in earlier versions [1]. Therefore, under zsh older than 5.1, quoting is required. This manifested as random «builtin=''» in emitted to the terminal, and commands (such as 'echo') highlighted as errors (in red). [1] https://github.com/zsh-users/zsh/blob/master/README#L46 (the section "Incompatibilites between 5.0.8 and 5.1")pull/190/head