How does xtb constrain multiple bonds during the MD process?

[Eudaimonia18]

I need to constrain the distances between multiple atoms during the MD process. The 'constrain' section in the manual provides examples for constraining a single bond length, bond angle, or dihedral angle. I attempted to apply constraints to multiple atoms and increased the constraint force. Below is my input file:

$constraint
force constant=2.0
distance: 2, 9, 1.45
distance: 5, 6, 1.45
distance: 60, 61, 1.45
distance: 57, 64, 1.45
$end

However, it seems that the code isn't working as intended. I don't see a dedicated section listing bond lengths in the output file, similar to what's shown in the manual. Moreover, during the MD trajectory, I've observed significant deviations of these bonds from their preset values. In other discussions, I've come across methods where people indirectly achieve the constraint of multiple bonds by invoking xtb through programs like Orca (http://bbs.keinsci.com/thread-39106-1-1.html).

How should I structure the input file to constrain the distances between multiple atoms in xtb?

Thank you

[Eudaimonia18]

I carefully examined my input file and conducted tests, and I found that $constraint should be $constrain.

In newer versions of xtb (such as 6.7.1), the information related to constraints is written in the output file as :

4    8 O      105

constraining bond 2 9 to 1.4500000 Å, actual value: 1.4514170 Å
constraining bond 5 6 to 1.4500000 Å, actual value: 1.4520452 Å
constraining bond 60 61 to 1.4500000 Å, actual value: 1.4643481 Å
constraining bond 57 64 to 1.4500000 Å, actual value: 1.4648622 Å
spherical wallpotential with radius 11.6941115 Å

       -------------------------------------------------
      |                Calculation Setup                |
       -------------------------------------------------

It appears that multiple bonds have been successfully constrained.