The optional thickness attribute is the line thickness in pixels.
Source
<xs:element name="LineStyle" type="LineStyleType" default="SOLID" minOccurs="0"><xs:annotation><xs:documentation>The optional LineStyle element is the line style of the auxiliary line.</xs:documentation></xs:annotation></xs:element>
The optional size attribute defines a recommended size for visualization of an infinite drawable element such as plane, cylinder, axis, etc., or objects without explicit geometric parameters (e.g. coordinate system).
The optional transparency attribute defines the transparency property of a model entity.
Source
<xs:complexType name="LineAuxiliaryType"><xs:annotation><xs:documentation>The LineAuxiliaryType defines an auxiliary line.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="AuxiliaryBaseType"><xs:sequence><xs:group ref="LineSegmentGroup"><xs:annotation><xs:documentation>The LineSegmentGroup is a group of elements that contains a start point and an end point that define a portion of a line.</xs:documentation></xs:annotation></xs:group><xs:element name="LineStyle" type="LineStyleType" default="SOLID" minOccurs="0"><xs:annotation><xs:documentation>The optional LineStyle element is the line style of the auxiliary line.</xs:documentation></xs:annotation></xs:element></xs:sequence></xs:extension></xs:complexContent></xs:complexType>