Thank you for writing us.
RadToolStripItem has a specific overflow behavior of its children elements. When you drag and drop a toolstrip item and there is not enough space for a child element, the child element goes into hidden state. If you increase the size of the toolstrip item, the child element goes to visible state. Because of this, the behavior to custom set the visibility of any children elements of RadToolStripItem is not supported.
This nevertheless sounds like a good feature and we will consider redesigning RadToolStrip to support this.
If you have questions please feel free to write me.
the Telerik team
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