logback-android/src/main/java/ch/qos/logback/core/subst/Parser.java
private Node C() throws ScanException {
    Node e0 = E();
    Token t = peekAtCurentToken();
    if (isDefaultToken(t)) {
      advanceTokenPointer();
      Node literal = makeNewLiteralNode(CoreConstants.DEFAULT_VALUE_SEPARATOR);
      e0.append(literal);
      Node e1 = E();
      e0.append(e1);
    }
    return e0;
  }
private Node C() throws ScanException {
    Node e0 = E();
    Token t = peekAtCurentToken();
    if (isDefaultToken(t)) {
      advanceTokenPointer();
      Node literal = makeNewLiteralNode(CoreConstants.DEFAULT_VALUE_SEPARATOR);
      e0.append(literal);
      Node e1 = E();
      e0.append(e1);
    }
    return e0;
  }
C = E(':='E|~)