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Recently I began validating HTML 4.0 Strict pages by direct input, as opposed to uploading them and then checking by URI. Several files were passed as clean on direct input. But the same files, once installed on my Web site, failed validation by URI with a single error: <IMG> tag not enclosed in a block element. The actual error message is: "document type does not allow element "IMG" here; missing one of "P", "H1", "H2", "H3", "H4", "H5", "H6", "DIV", "ADDRESS" start-tag." It seems to me that this is the sort of error that should be picked up by the validator no matter which input method is used. Searching did not disclose any previous instance of this bug. I've since fixed the problem in the on-line files. If you need a test case, let me know and I'll re-create it.
A test case would be welcome indeed. Thank you!
[after receiving a test case by private mail] passing this page directly to the validator and passing it by copy-pasting the source into the "direct input" validation gives me exactly the same result. I'm suspecting the source code you sent to the validator by "direct input" and "by URI" may have been different. Use the "view source" option of the validator to see what the difference may be.
I found the same thing when I tried my test case -- that is, direct input gave the same error as check by URI. I guess this bug is invalid. But it is puzzling, because the problem arose when I found several other errors in the original HTML file by direct input, fixed those, got it to validate, uploaded it, and then saw the error message I reported here. Ah, I see I can invalidate the bug myself. I'll do that thing.