tspan()
Produces an SVG "tspan" element.
Syntax
tspan(
   x DECIMAL,
   y DECIMAL,
   dx STRING,
   dy STRING,
   style STRING,
   content STRING )
  RETURNS om.DomNode
- x defines the X position of the tspan element.
 - y defines the Y position of the tspan element .
 - dx defines the delta-X for horizontal positioning of the tspan element.
 - dy defines the delta-Y for vertical positioning of the tspan element.
 - style defines the in-line style to be applied on the tspan element.
 - content is the actual text.
 
Usage
This function creates a "tspan" SVG DOM element from the parameters.
A tspan element can be used to draw multiple lines of text in SVG.
The DOM nodes created by this function must be added to a "text" element
produced by the text() function.
Example
DEFINE root_svg, t om.DomNode
...
LET t = fglsvgcanvas.text(NULL,200,NULL,"style_2")
CALL root_svg.appendChild( t )
CALL t.appendChild( fglsvgcanvas.tspan(120,NULL,NULL,30,NULL,"First line" ) ) 
CALL t.appendChild( fglsvgcanvas.tspan(120,NULL,NULL,30,NULL,"Second line" ) )