If you give a PI marker type a name that starts with Table, Row, or Cell, DITA2Go uses the content of the marker for the value of whatever HTML attribute is designated by the rest of the PI marker-type name, and puts the attribute and its value in the generated <table>, <th>, <tr>, or <td> tag. An attribute value assigned with a PI marker takes precedence over values of the same attribute assigned any other way; see Table 33-1.
For example, to guarantee that a certain table cell is top-aligned in HTML regardless of its properties in DITA or any properties assigned in the configuration file, you could insert a PI marker of type CellValign just before the cell in DITA, and make the content of that marker top. In HTML, the resulting tag for that cell would be <td valign="top">.