/** check whether only one given tag exists and matches <code>sTextReg</code> */
protected boolean checkTagText(Element parent, String sTag, String sTextReg, boolean bSilent)
{
Element elem = getOneTag(parent, sTag, bSilent);
if (elem == null) { return false; }
String sText = elem.text();
sText = sText.replace('\u00a0', ' ');
if (!sText.matches(sTextReg)) {
println(PbnTools.getStr("error.invalidTagValue", sTag, sTextReg, elem.text()));
return false;
}