Mesh classes will be very complex in a fluid system such as Susie, because context is important. We do not provide it by default (for now). I quickly whipped it, and it should close you:
@mixin susy-classes($silent: false) { $base: if($silent, '%', '.'); $selector: '#{$base}span'; @if $silent {
It could be a little cleaner if it were added to Susy's core, but for now it should cover your needs. It will output either silent classes for extension or standard classes. Let me know how this works for you, and feel free to report a problem on github to consider moving this to the kernel.
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