This is place where the mesh's viewport representation is controlled.
Visible
Toggle the mesh's visibility.
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Here you can visualize the active → particle channels as a gradient map. To see the channel please enable the “Smooth Shaded” mode with the 0 key.
Transparency
The mesh Mesh visibility can range from opaque (0.0) to completely transparent (1.0). This feature does not work when a “Particle channel” or “Render as points” is active.
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With this mode, only the mesh's vertices will be displayed. Their size can be controlled with the associated “@ Points size” parameter.
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Point size
When “Render as points” is active only the mesh's vertices will be displayed and here you can control their size.