"algorithm, defined in FITS-WCS paper III, should be used if at all possible when writing out a FrameSet using the FITS-WCS encoding.
Note this attribute has no effect unless the TabOK attribute is set to a positive non-zero value. If, in addition to setting TabOK, ForceTab is set to non-zero value, astWrite will attempt to use the
TAB algorithm even if another algorithm could have been used. If ForceTab is left at its default value of zero, then the -TAB algorithm will be used only if no other algorithm can be used.