Every time we call `XemblyLine#log()` a new line appears in logs. This line contains Xembly instructions. In any moment of time we can parse the entire log and select Xembly instructions from it, one by one. Then, we apply these instructions to an empty `<snapshot/>` XML document.

In this case, on every `#charge()` call we report a new Xembly log line that contains a few instructions that increment `/snapshot/cost` element. Thus, the resulting snapshot will have an accumulated value.

Makes sense?