TruncatedBounds.swift

// It's possible that the text is truncated not because of the line break mode,
// but because the text is outside the drawable bounds
if isTruncating == false {
  // This gives us the range of all the characters that have been already laid out
  // into the text container by the layout manager. 
  let glyphRange = layoutManager.glyphRange(for: textContainer)
  
  // This provides the range of glyphs (not characters) that have been generated for the text container.
  // Since a glyph is a graphical representation of a character, and more than one glyph can be used 
  // to represent a single character, this should always be equal or greater than the number of
  // characters within the text container's layout buffer.
  let characterRange = layoutManager.characterRange(forGlyphRange: glyphRange, actualGlyphRange: nil)

  // If it is indeed less than the amount of characters we have in the text then that means
  // the `UITextView` is not currently displaying all of its text content within its bounds.
  isTruncating = characterRange.upperBound < text.utf16.count
}