The element <spanspec> (span specification) identifies a horizontal span of columns and associated attributes that can subsequently be referenced by its attribute spanname for repeated use in a table’s <entry> elements. A <spanspec> uses column names from <colspec> elements defined in that context. It gets default values from the <colspec> that provides the namest. namest and nameend identify the first and last columns in increasing left-to-right order that identify the span. The reason colname is used rather than colnum in identifying <spanspec> is that the names are independent of revisions that can change the number of inserted/deleted columns, as long as namest remains to the left of (has a smaller column than) nameend. In a <thead> or <tfoot>, if any <colspec> are redefined, the <tgroup> <spanspec> elements are ignored in references to spanname from <entry> elements within this <thead> or <tfoot>. When such redefinition occurs, any spanning should be by the attributes namest and nameend.