Useful XML Syntax

Standard XML placeholders can be used to simplify some scripts. For example, the following (abbreviated) code ensures that the limits of a domain are symmetric.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE simulation [
<!ENTITY Npts    "64">
<!ENTITY L      "3.0e-5">
]>
  <simulation xmds-version="2">

    . . .

    <geometry>
        <propagation_dimension> t </propagation_dimension>
        <transverse_dimensions>
          <dimension name="x" lattice="&Npts;"  domain="(-&L;, &L;)" />
        </transverse_dimensions>
     </geometry>