Question about Rich Text Box

You have to know the Rich Text Format(RTF) to be able to manually modify the text in an RTF buffer.
An RTF table is defined as a collection of rows that contain cells.
 

An example;
|---------------------------|
|  Row1Cell1  | Row1Cell2   |
|---------------------------|
 
The corresponding RTF is;
{
  \trowd \trgraph180
  \cellx1440\cellx2800
  \pard\intbl Row1Cell1 \cell
  \pard\intbl Row1Cell2 \cell  
  \trow
}

 
The curly brackets are optional and added for readability
\trgraph180 - This row has cells with internal margins of at least 180 twips
\cellx1440\cellx2800 - This row contains 2 cells the fist ends at 1440 twips from left margin and the second 2800 twips from left margin.
\pard\intbl Row1Cell1 \cell - Cell contents
\pard\intbl Row1Cell2 \cell - Cell contents