Here is our you would add 21 as default value for 21% of VAT.
Code:
$HD_Form -> AddEditElement (gettext("VAT"),
"vat",
"",
"INPUT",
"size=10 maxlength=6 value='21'",
"12",
gettext("Insert the number for the VAT"),
"" , "", "", "", "", "", "NO-NULL" , gettext("VAT to add on the invoice of this customer. it should be a decimal value '21' this will be for 21% of VAT!"));
You can make it fancier by reading the default value from the configuration file (a2billing.conf). I will assume that the constant DEFAULT_VAT will be created in Class.A2billing.php in the same fashion the other constants are set using config options.
Code:
$default_vat = DEFAULT_VAT
$HD_Form -> AddEditElement (gettext("VAT"),
"vat",
"",
"INPUT",
"size=10 maxlength=6 value='{$default_vat}'",
"12",
gettext("Insert the number for the VAT"),
"" , "", "", "", "", "", "NO-NULL" , gettext("VAT to add on the invoice of this customer. it should be a decimal value '21' this will be for 21% of VAT!"));
Cheers