js正则表达式：替换一个单词不是后跟或后面没有单词

I want to replace the "word" that is outside "span", and keep the other that is inside "span". By now, the following code works when both are following "mark>" and followed by "span". But I want to go further, following "mark>" OR being followed by "span", any one of the two condition should cause replacing action.I want to replace the "word" that is outside "s