code: public boolean isActive(final org.apache.tools.ant.Project p) {
      if (p == null) {
        throw new NullPointerException("p");
      }
      if (this.ifCond != null) {
        final String ifValue = p.getProperty(this.ifCond);
        if (ifValue != null) {
          if (ifValue.equals("no") || ifValue.equals("false")) {
            throw new BuildException("property " + this.ifCond + " used as if condition has value " + ifValue
                + " which suggests a misunderstanding of if attributes");
          }
        } else {
          return false;
        }
      }
      if (this.unlessCond != null) {
        final String unlessValue = p.getProperty(this.unlessCond);
        if (unlessValue != null) {
          if (unlessValue.equals("no") || unlessValue.equals("false")) {
            throw new BuildException("property " + this.unlessCond + " used as unless condition has value " + unlessValue
                + " which suggests a misunderstanding of unless attributes");
          }
          return false;
        }
      }
      if (isReference()) {
        final LibrarySet master = (LibrarySet) getCheckedRef(LibrarySet.class, "LibrarySet");
        return master.isActive(this.project);
      }
      if (this.libnames.length == 0) {
        p.log("libnames not specified or empty.", Project.MSG_WARN);
        return false;
      }
      return true;
    }
docs: Returns true if the define's if and unless conditions (if any) are
  satisfied.