Coming in WordPress 4.7: New Visible Edit Shortcuts in the Customizer
#27403 added visible edit shortcuts to the customizer preview, making it easier to see which elements of your site are editable in the customizer and how to edit them. Here’s a demo with Twenty Fifteen (note that the ability to toggle icons off has since been removed): Implementation: Selective Refresh Partials
Visible edit shortcuts are an extension of the existing “shift-click-to-edit” functionality built into customizer partials. Partials are sections of the front end of the site, in the customizer preview, that are associated with customizer settings. When settings change, their associated partials are selectively refreshed via an Ajax call without reloading the entire preview. Partials are to the customizer preview what controls are to the customizer editing pane: a visual representation of a setting.
Buttons are now injected into partials within the preview to expose this relationship visually and to users of all input modes. However, the role of the customizer preview is to provide an accurate representation of the frontend of the site as it’ll appear once changes are published. Accordingly, visible edit shortcuts pose a challenge as they have the potential
Source: https://managewp.org/articles/13819/coming-in-wordpress-4-7-new-visible-edit-shortcuts-in-the-customizer
source https://williechiu40.wordpress.com/2016/11/11/coming-in-wordpress-4-7-new-visible-edit-shortcuts-in-the-customizer/