The alignment may be tricky and this function therefore simplifies this process by extending/shortening the alignment to match the correct number of columns.
prPrepareAlign(align, x, rnames, default_rn = "l")The matrix/data.frame with the data. For the print and knit_print
it takes a string of the class htmlTable as x argument.
Default row names are generated from rownames(x). If you
provide FALSE then it will skip the row names. Note: For data.frames
if you do rownames(my_dataframe) <- NULL it still has
row names. Thus you need to use FALSE if you want to
supress row names for data.frames.
The default rowname alignment. This is an option as the header uses the same function and there may be differences in how the alignments should be implemented.
Other hidden helper functions for htmlTable: 
prAddCells(),
prAddEmptySpacerCell(),
prAddSemicolon2StrEnd(),
prEscapeHtml(),
prGetCgroupHeader(),
prGetRowlabelPos(),
prGetStyle(),
prPrepInputMatrixDimensions(),
prPrepareCgroup(),
prTblNo()