What is ⌥ Option keyboard shortcut for?

Adobe Photoshop (macOS) - (Click Clear History in History panel pop‑up menu) Permanently clear history (no Undo)  

Adobe Photoshop (macOS) - (Use Merge Down command from the Panel pop‑up menu) Copy current layer to layer below  

Adobe Photoshop (macOS) - (Use Merge Visible command from the Panel pop‑up menu) Merge all visible layers to a new layer above the currently selected layer  

Adobe Photoshop (macOS) - (Click the eye icon) Show/hide all other currently visible layers  

Adobe Photoshop (macOS) - Change Cancel to Reset  

Adobe Photoshop (macOS) - (Click Edge Highlighter/Eraser tool) Toggle between Edge Highlighter tool and Eraser tool  

Adobe Illustrator (Mac) - Switch to Smooth tool while using Blob Brush tool  

Adobe Illustrator (Mac) - Switch between Direct Selection tool and Group Selection tool  

Adobe Illustrator (Mac) - Switch Pen tool to Convert Anchor Point tool  

Adobe Illustrator (Mac) - Switch between Add Anchor Point tool and Delete Anchor Point tool  

Adobe Illustrator (Mac) - Switch Scissors tool to Add Anchor Point tool  

Adobe Illustrator (Mac) - Switch Pencil tool to Smooth tool  

Adobe Illustrator (Mac) - Switch between Area Type and Path Type, Vertical Area Type and Vertical Path Type tools  

Procreate 5X - Activate the Modify button in the sidebar  

Corel Painter (Mac) - Dropper  

Corel Painter (Mac) - Set clone source  

Corel Painter (Mac) - Dropper  

Corel Painter (Mac) - Subtract from selection  

Pixelmator Pro - (Hold down the Option key before starting to select) Subtract from a selection  

Pixelmator Pro - Press and hold the Option key before starting to draw: Subtract a shape from the selected shape  

Sketch - (resize while holding) Resize from center  

Framer X - Show Distance  

Aseprite 1.2.27 (macOS) - (when moving) Snap to grid  

Aseprite 1.2.27 (macOS) - Rotate  

Adobe XD (Mac) - Asymmetric Control Point  

Adobe XD (Mac) - From Center  

Adobe XD (Mac) - (with an object selected) Enable measurements  

Adobe Photoshop Elements (Mac) - (use Merge Down command from the panel pop-up menu) Copy current layer to layer below  

Adobe Photoshop Elements (Mac) - (use Merge Visible command from the panel pop-up menu) Copy all visible layers to active layer  

Adobe Photoshop Elements (Mac) - (on any painting tool or shape tool, except Impressionist Brush) Switch to Eyedropper tool  

InVision (macOS) - (hover) Measure Distance To Hovered Item