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Select Text in Quick Look Windows
To activate the setting, open a Terminal window and type the following:
defaults write com.apple.finder QLEnableTextSelection -bool TRUE;killall Finder
The changes take effect immediately. To deactivate the setting, open a Terminal window and type the following:
defaults delete com.apple.finder QLEnableTextSelection;killall Finder
Funciona apenas nas janelas do Finder. Qual eu acho que é o que você está depois. Confirmado no Leão.