A clipping mask lets you use the content of a layer to mask the layers above it. Content of the bottom or base layer determines the masking. The non-transparent part of the base layer clips (reveals) the content of the layers above it in the clipping mask. All other content in the clipped layers is masked out (hidden).
You can use multiple layers in a clipping mask, but they must be successive layers. The name of the base layer in the mask is underlined, and the thumbnails for the overlying layers are indented. The overlying layers display a clipping mask icon.
The Blend Clipped Layers As Group option in the Layer Style dialog box determines whether the blending mode of the base affects the whole group or just the base. (See Group blend effects.)

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To add additional layers to the clipping mask, use either of the methods described in the step 2 and work your way upward one level at a time in the Layers panel. Layers in the clipping mask are assigned the opacity and mode attributes of the base layer.
If you create a layer between layers in a clipping mask, or drag an unclipped layer between layers in a clipping mask, the layer becomes part of the clipping mask.
- Hold down Alt (Win) or Option (Mac), position the pointer over the line separating two grouped layers in the Layers panel (the pointer changes to two overlapping circles
), and click.