The ExtractAllowedHeads command returns a description of OpenMath symbols that are accepted as heads from the server's raw reply.  The users can get the raw reply by specifying output = xml when the initial request is made.

NULL is returned if the reply from the server contains an error or is not a "procedure completed" message.

Note that this command is intended for advanced users of the package who wish to examine the reply in SCSCP format.  Normal users do not need this command.

$\mathrm{with}\left(\mathrm{SCSCP}\right)\:$

$\mathrm{with}\left(\mathrm{Client}\right)\:$

$\mathrm{result}≔\mathrm{GetAllowedHeads}\left(''myfavorite.scscpserver.com''\,'\mathrm{output}'='\mathrm{xml}'\right)\:$

$\mathrm{XMLTools}\left[\mathrm{Print}\right]\left(\mathrm{XMLTools}\left[\mathrm{ParseString}\right]\left(\mathrm{result}\right)\right)$

  <OMOBJ>
     
    <OMATTR>
       
      <OMATP>
         
        <OMS cd = 'scscp1' name = 'call_id'/>
         
        <OMSTR>Hfq6mjRpov2011-01-2711:11:15</OMSTR>
         
        <OMS cd = 'scscp1' name = 'info_memory'/>
         
        <OMI>124248</OMI>
         
        <OMS cd = 'scscp1' name = 'info_runtime'/>
         
        <OMI>0</OMI>
         
      </OMATP>
       
      <OMA>
         
        <OMS cd = 'scscp1' name = 'procedure_completed'/>
         
        <OMA>
           
          <OMS cd = 'scscp2' name = 'symbol_set'/>
           
          <OMS cd = 'scscp_transient_maple' name = 'GeneralMapleService'/>
           
          <OMS cd = 'scscp_transient_maple' name = 'IntegerFactorization'/>
           
        </OMA>
         
      </OMA>
       
    </OMATTR>
     
  </OMOBJ>

$\mathrm{ExtractAllowedHeads}\left(\mathrm{result}\right)$

$\left[\left[''scscp\_transient\_maple''\&comma;''GeneralMapleService''\right]\&comma;\left[''scscp\_transient\_maple''\&comma;''IntegerFactorization''\right]\right]$