How to add a Header and Tabs to XML data file in SAS code?

Hello,
I am trying to add a header and tabs with info about the XML data file to .xml file in SAS code. How exactly this can be done? Please see what I have currently I have for my SAS code. I can see the XML data file as my output but the Header (tab and tab2) with all info about the XML file does not show up yet in the XML file.
 

libname xmldir xmlv2 '/basepath/examples/XMLData.xml' xmltype=generic;

/* Req. 1: Macro variables to provide appropriate tab spacing. */
%let tab="    ";
%let tab2="        ";

/* Req. 2: XML file information and header*/
data _null_;
   file xmldir;
  
    put '<?xml version="1.0" encoding="UTF-8"?>';
    put '<Schema Name>';
    put &tab. '<Header>';
    put &tab2. '<SampleDate>2017-06-14</SampleDate>';
    put &tab2. '<CaseCount>30</CaseCount>';
    put &tab2. '<Action>Initial</Action>';
    put &tab2. '<YearPeriod>2017</YearPeriod>';
    put &tab. '</Header>';
    put &tab. '<Payload>';
run;

/* Req. 3: Writing two SAS datsets to xmldir library and creating XMLData.xml data file*/ 
data xmldir.dataname1(label="dataset name1 from sashelp library");
       set sashelp.dataset1(obs=10);
run;

data xmldir.dataname2(label="dataset name2 from sashelp library");
       set sashelp.dataset2(obs=20 keep=var1 var2); 
run; 

libname xmldir clear;

/* Req. 4: XML File End*/
data _null_;
   file xmldir mod;

    put &tab'<Payload>';
    put '</Schema Name>';
run;

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So, currently only Req. 3 is working.
Any comments or suggestions will be greatly appreciated!