isComposingRangeValid property
Whether the composing range is a valid range within text.
Returns true if and only if the composing range is normalized, its start is greater than or equal to 0, and its end is less than or equal to text's length.
If this property is false while the composing range's isValid is true,
it usually indicates the current composing range is invalid because of a
programming error.
Implementation
bool get isComposingRangeValid => composing.isValid && composing.isNormalized && composing.end <= text.length;