help needed with xpath and selenium

selenium IDE gave me following xpath for string on page called "System". However this string may appear somewhere other than this place in future.

//ul[@id='idCTree_sor_ul']/li/ul/li[23]/span

how can I rewrite above xpath by spcifying text()="System" in xpath , so in future if index of that string is moved would not impact on my xpat开发者_如何学运维h

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//span[./text() = 'System']