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Italics support is coming to the iTerm2 terminal app - it's in the nightly builds now.
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Or, to customize the syntax highlighting locally to format comments in italics, add the following to your vimrc file: highlight Comment cterm=italic Then make sure the font you use supports italics and also your colorscheme contains italic for some syntax parts. To work around this in Vim, add the following to your vimrc file to define the terminal commands for enabling/disabling italics: let &t_ZH="\e[3m"
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As of OS X Sierra 10.12, the default terminal app supports italics however, the included version of ncurses contains xterm terminfo files that do not declare italic support (they do not define the sitm capability).
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