guideY(y)
Creates a horizontal guide line at the current spread and current layer.
Type: function
Parameter(s):
- y {Number}:
Position of the new guide line.
 
Returns:
- 
    {Guide}:
New guide line.
 
Creates a horizontal guide line at the current spread and current layer.
Type: function
Parameter(s):
Position of the new guide line.
Returns:
New guide line.