Returns the starting offset (character position) of the composition relative to the target if a composition is occurring, or zero if there is no composition in progress.
This property is read-only.
result = object.compositionStartOffset
Type: unsigned long
For compositions occurring on an input or textarea element, the compositionStartOffset is the starting offset of the composition within the target's value string. For compositions occurring on an element with the contenteditable flag set, compositionStartOffset returns the starting offset relative to the target's textContent property.