"The world is your oyster, and you are its pearl." This proverb, in many little variants, is so well known in English that it is often twisted around into fresh forms. In nature, if an everday oyster gets a speck of grit in its shell, it can produce a beautiful and valuable pearl around that grit. So, symbolically, you get something of great value in a commonplace setting. Here, the writer is being sarcastic. He wants people to use simple, coherent designs for web pages. But he knows he has no control, so he says "if you don't want your page to look good", then you can pick and choose from everything in the world - which echoes from "the world is your oyster". But just to make sure the reader understands his disapproval, he calls it an "ugly oyster". Incidentally, one line of humour in English comes from accidentally or deliberately misusing words, and there is an example here. A corruption of this phrase is when a character says "the world is my lobster" - usually a deliberate misuse, but still designed to emphasise the speaker's status as "the pearl." I hope this helps. So, to question 1 : there is a specific meaning, as explained here. Question 2 : "oyster" is a safe word to use; it's just a shellfish. Speaking symbolically always carries extra risk of being misunderstood.