From the help file
Click on Line Style in order to enter an attribute expression for calculating the line style for the line or line segment associated with the data point. This type of attribute expression only has effect on line, combo and radar charts.
The relative width of the line can be controlled by including a tag <Wn> where n is a multiplying factor to be applied on the default line width of the chart. The number n must be a real number between 0.5 and 8. Example: <W2.5>. The style of the line can be controlled by including a tag <Sn> where n is an integer between 1 and 4 indicating the style to be used (1=continuous, 2= dashed, 3=dotted, 4=dashed/dotted). Example: <S3>. The <Wn> and <Sn> tags can be freely combined, but only the first occurrence of each counts. The tags must be enclosed by single quotations.
