use WWW::Mechanize;
   my $mech = WWW::Mechanize->new();
$mech->get("$mydomain/post.php");

$mech->form_number(2);
$mech->field("headline","MyHeadline"); 
$mech->field("thecontent","MyContent"); 
$mech->field("categories[some_tag]","Blah"); 
$mech->click("publish");
[download]

HTML code is too large. Line in question is:

<input type="text" name="categories[some_tag]" class="categories form-
+input-tip" size="16" value="Add Word" />
[download]