Division lines in tables

[geert@jet.es]

I am trying to understand the logic behind the "division lines" that can be used to underline certain columns in a table.

As far as I understood :

\DC just jumps to the next column
\DL draws a line under the actual column and skips the next column.
\DL[n]draws a line under n columns, starting with the actual one, and skips the column that comes after the end of the drawn line
\DR ends the division line.

Below is an extract from a 17 column table, where I want to draw rectangles around the words (except the last one) that works fine:

\steltabellenin[korps=6pt]
\plaatstabel[forceer][] 
{}
\starttabel[|c|c|c|c|c|c|c|c|c|c|c|c|c|c|c|l|l|]

\DL          \DL          \DL          \DL          \DL          \DL           \DL           \DL               \DC            \DR
\VL col1 \VL \VL col3 \VL \VL col5 \VL \VL col7 \VL \VL col9 \VL \VL col11 \VL \VL col13 \VL \VL col15 \VL     \NC col17  \LC \MR
\DL          \DL          \DL          \DL          \DL          \DL           \DL           \DL               \DC            \DR
\stoptabel

But now comes an extract from the same table, where I want to underline columns  number 1, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14 and 15:

\steltabellenin[korps=6pt]
\plaatstabel[forceer][] 
{}
\starttabel[|c|c|c|c|c|c|c|c|c|c|c|c|c|c|c|l|l|]

\FC txt1 \NC \NC      \NC \NC THREE{\bf tekst2} \NC \NC      \NC \NC       \NC \NC \TWO{txt3}\NC       \NC     \NC        \LC \FR
\DL          \DL[7]                                              \DL[5]                                        \DC        \DC \DR
\stoptabel

The funny thing about this part of the table is, that the log file tells me that one tab was replaced by a cr because there were too many of them, the table looks OK in my PDF document, but the page numbering is wrong.

When I delete the last \DC before the \DR, the table complains about a missing column and does not print correctly.

Any clues ?  I probably did not grasp the logic behind this division lines, so a concise explanation of how this works is also welcome.

Geert Dobbels.