tidy-html5/README/MESSAGES.md

Message System

Tidy has quite complex warning/error messaging system. This is all about adding a new warning or error message to libTidy.

First assign the message a key value. This is done in message.h, in one of the two enumerations that are listed there.

1. tidyErrorCodes - starts with the value CODES_TIDY_ERROR_FIRST = 200, and it must be first.

2. tidyMessagesMisc - starts with the value ACCESS_URL = 2048 - so, at present the above tidyErrorCodes must not exceed this.

3. For the sake of completeness, there's also a third enum present in access.h called accessErrorCodes; you should only ever be concerned about this if you are working on new strings for Tidy's accessibility module.

If your message is something that will appear in the error list, then its key should be defined in the tidyErrorCodes enum, unless you are adding errors to the accessibility module (see point 3, above). If you are adding strings that are not intended for the error list, then they belong in tidyMessagesMisc. These are strings that are typically output with Tidy's CLI.

All enum values are only ever used by name within libTidy (and incidentally, should only ever be used by name in your client applications; never trust the value!), so feel free to enter new strings wherever they make the most sense. There are already existing categories (marked by comments), or feel free to create a new category if that's best.

Because some clients retrieve error information via libTidy’s callback mechanism, it's also important to update the language.c:tidyErrorFilterKeysStruct[], as well, if your new messages are intended for the error list.

Step 1

So in this case I want to add 3 warning messages: BAD_SURROGATE_PAIR, BAD_SURROGATE_TAIL, and BAD_SURROGATE_LEAD. Because these are error messages, they belong in the tidyErrorCodes enum, and they fit into nicely into the "character encoding errors" category just before the last CODES_TIDY_ERROR_LAST.

Step 2

Because the new messages are error code, update the tidyErrorFilterKeysStruct in language.c with the same key values, and with string representations thereof. You should put them in the same logical order as you inserted them into tidyErrorCodes enum.

Note that at some point when all of the error enums are merged (probably Tidy 5.5) this kludge won't have to be used and we can have a nice, single enum exported to clients.

Step 3

The next step is adding a format string to language_en.h. This string may later be translated to various supported language strings, but at present it is important that the other language translated strings, like language_fr.h, language_es.h, etc, keep the same format order.

Where to add this seems a bit of a mess, but in general things are grouped by where they're used in libTidy, and often in alphabetical order within those groups. Here I've added them relative to where they were placed in the other enums and structs.

Depending on which of the output routines you use (consult message.c) you may be able to use parameters such as %u and %s in your format strings. The available data is currently limited to the available message output routines, but perhaps generalizing this in order to make more data available will be a nice focus of Tidy 5.5. Please don't use printf for message output within libTidy.

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