There's an interesting set of options for the weird "xadder" token: misspellings of "xpadder" (a game pad helper), xadder (the name of at least two or three tools), xadder (a parameter in an XLib call), XAdder (the Xilinx full adder implementation for the Vivado FPGA platform), and more than a few usernames on various forums.
Importantly, though, the token is "\\xadder" which looks a bit like an escaped hex code. That actually suggests a different origin of the token. `\xad` is the Unicode soft-hyphen (U+00AD). The soft hyphen is used to suggest where it makes sense to hyphenate a word if a line-break is needed. This shows up fairly frequently (2.9k occurrences) on GitHub in web-scraping datasets, which suggests that a model trained on data scraped from the web might see a fair number of these.
Basically, OpenAI is trained on web data that has a number of words where splitting on -der makes sense (e.g., mur-der, un-derstanding, won-derful; although the most common occurrence in a GitHub search for "\\xadder" is what appears to be an incorrectly encoded string "L\xc3\xadder", probably from the Portuguese and Spanish "Lí-der").
Anyways, using the o200k tokenizer `mur\xadder` yields two tokens (88762 and 179582). 88762 encodes "mur" and 179582 encodes "\xadder".
