textKerning([kerning])
Returns the current kerning and sets it if argument kerning is given.
Type: function
Parameter(s):
- kerning {Number} Optional:The value to set. 
Returns:
- 
    {Number}:
 The current kerning. 
Returns the current kerning and sets it if argument kerning is given.
Type: function
Parameter(s):
The value to set.
Returns:
The current kerning.