code: @SuppressWarnings(UNUSED)
      public FormValidation doCheckIvySettingsFile(@QueryParameter String value) {
          String v = Util.fixEmpty(value);
          if ((v == null) || (v.length() == 0)) {
              // Null values are allowed.
              return FormValidation.ok();
          }
          if (v.startsWith("/") || v.startsWith("\\") || v.matches("^\\w\\:\\\\.*")) {
              return FormValidation.error("Ivy settings file must be a relative path.");
          }
          return FormValidation.ok();
      }
docs: Stapler URL binding used by the configure page to check the location of
  alternate settings file.
  
  @param value file to check
  @return validation of file