Without the presence of a <?blockcolspec>, all column properties are set with <?blockcol*> commands. Each individual column property is propagated independently from the others, until every column has a value (see <?blockcolwidth> to see how the propagation works). To override a property within a single column, either the block must be prescanned and the property specified within the data for the column; or the property must be specified for all the intervening columns too.

All of this is still true if no <?blockcolspec> commands are encountered. The <?blockcolspec> command lets you specify that all column commands apply to a given column, until a new <?blockcolspec> command is encountered. In addition, any cell commands (<?blockcell*>) will provide the default cell properties for the designated column.

When PTC ALD finds the first <?blockcolspec> command in a table, all the same propagation of column properties takes place as before, setting up the default column properties. In addition the default cell properties for the table are built from the current cell state. Whenever a new <?blockcolspec> command is encountered, these properties will be reinstated as the defaults to be overridden if desired.

If colnum is specified it designates which column is currently being defined, with 1 being the first column.

If repeat is specified it defines the number of columns that will have the same default. Note this is identical to specifying <?blockcolrep=repeatnumber> just after the <?blockcolspec> command.