The HitTestKey property indicates the key associated to the part of the element from the cursor. The Element property specifies the Element from the cursor. The HitTestCode property specifies the code where the cursor hovers the element. 

The HitTestKey may returns one of the following values, based on the HitTestCode property as listed:

• nothing, if HitTestCode property is exHitTestMargin, exHitTestStatus, exHitTestClient and exHitTestGlyph.
• the identifier of the icon/picture from the cursor if HitTestCode property is exHitTestPicture.
• the element's caption if HitTestCode property is exHitTestCaption.
• the element's extra-caption if HitTestCode property is exHitTestExtraCaption.
• element's Checked property, if HitTestCode property is exHitTestCheckBox.