@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
  public TextLayoutBuilder setLetterSpacing(float letterSpacing) {
    if (getLetterSpacing() != letterSpacing) {
      mParams.createNewPaintIfNeeded();
      mParams.paint.setLetterSpacing(letterSpacing);
      mSavedLayout = null;
    }
    return this;
  }
Sets text letter-spacing in em units. Typical values for slight expansion will be around 0.05.
Negative values tighten text.

@param letterSpacing A text letter-space value in ems.
@see #getLetterSpacing()
library/src/main/java/com/facebook/fbui/textlayoutbuilder/TextLayoutBuilder.java