The -validatecommand does not work if manually some text is written to the entry widget

See https://metacpan.org/pod/Tk::Entry#VALIDATION, by default no validation is performed

#!/usr/bin/perl --
use strict;
use warnings;
use Data::Dump qw/ pp /;
use Tk;
my $mw = tkinit;
$mw->Entry(
    -validate => 'all',
    -validatecommand => sub { 
        warn pp(\@_);
        return 1 if !length$_[0]
                    or $_[0] =~ m{^\d+$};
        return undef;
    },
)->pack;
$mw->MainLoop;
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Having spent a fair amount of time digging up all the relevant sections in Tk::Entry, so that you didn't have to read the entire documentation, I'm less than impressed that you chose to respond with nothing more than:

"The -validatecommand does not work if manually some text is written to the entry widget"

Kindly show an example of your code that demonstrates the"does not work" behaviour you describe. Ensure you include the part where you change the value of the -validate option from its default, as described in Tk::Entry - VALIDATION:

none

Default. This means no validation will occur.