code: public void addAssertion(String name, String value) {
          matchers.add(new AbstractMap.SimpleEntry<String, String>(name.trim(), value.trim()));
      }
docs: Add an assertion to this matcher where a {@link SLProperties} must have a property with the given name
  which at least contains the given value. Name and value are trimmed before matching is done.
  
  @param name the name of the property which must be present, must not be <code>null</code>
  @param value the value the property must at least contain, must not be <code>null</code>