For several days, Rick was fighting with a third party vendor. Rick's system was supposed to talk to his vendor's system using XML files, but their files were coming back with invalid XML data. Rick complained to a technical contact ("Terry") that the XML they returned was invalid. Terry argued that they were processing the file wrong.
The issue that Rick discovered was that one of the attribute values in the XML file used single quotes instead of double quotes. Terry insisted that the XML file used only double quotes, and made his case by sending over screenshots from XMLSpy and IE, showing that they were indeed double quotes. The screenshot from IE would've looked something like this:
"Yes, I see that," Rick replied via email, "but XMLSpy and IE both correct minor errors — for instance, changing single quotes to double quotes." Rick sent Terry a screenshot of the XML file in Notepad, which showed the attribute value with single quotes.
Later that day, Rick got a reply:
We have viewed these messages in XMLspy, Notepad and a IE browser, only Notepad shows this as ' the other 2 programs use ", we believe that this is just away that notepad translates these files. If required we are able to look at why Notepad translates these files with ' and not ", however this investigation will not be able to commence until early next week, although our thoughts are that the way that the file opens in notepad, has only clouded the issues... (snip)
Why Notepad has chosen to replace specific instances of double quotes with single quotes remains a mystery...