Sunday, July 19th, 2009
I see more and more people switch over to HTML5 these days, and to help you make sure you did things correctly, there are some tools at your disposal that might be good to know about.
To make sure you didn't misspell any tag or nest elements in a way that is not allowed, or find similar mistakes in your markup, you can use Validator.nu.
Alt text for images
The above-mentioned validator has a feature to help you quality-check your alternative text for your
img elements. Check the Show Image Report checkbox.
You can also disable images in your browser or try to use a text-only browser — the information that the images convey should still be available (but in text form). Sometimes an image doesn't convey any further information than what the surrounding text already says, and in such cases you should use the empty value:
For further advice and examples on how to use the
alt attribute, the HTML 5 spec has lots of information on the topic. If you're not going to read it all, just read the section called General guidelines.
The document outline is the structure of sections in the document, built from the
h6 elements as well as the new sectioning elements (
nav). The document outline is more commonly known as the Table of Contents.
To make sure that you have used the new sectioning elements correctly, you can check that the resulting outline makes sense with the HTML5 Outliner.
If you see "Untitled Section" and didn't expect them, chances are that you should have used
div instead of
If you have a subtitle of a heading that shouldn't be part of the document outline, you should use the
<h1>The World Wide Web Consortium</h1>
<h2>Leading the Web to Its Full Potential...</h2>
In this example, only the
h1 will show up in the document outline.
(This only applies to
table elements used for tabular data — not for layout.)
HTML tables have two types of cells: header cells (
th elements) and data cells (
td elements). These cells are associated together in the table: a data cell in the middle of the table can have associated header cells, typically in the first row and/or the first column of the table. To a user who can see, this association seems obvious, but users who cannot see need some help from the computer to understand which cells are associated with which.
You should mark up your header cells with the
th element and check that your cells get associated as you intended using the Table Inspector. If it isn't as you intended, you can consider simplifying or rearranging your table, or you can override the default association using
If you know about other tools for helping with quality assurance of HTML5, or if you have made your own, please share!
Posted in Conformance Checking | 4 Comments »
Sunday, May 18th, 2008
Kai Hendry has written an HTML filetype plugin for Vim that allows you to use Henri Sivonen’s Validator.nu conformance checking (validation) service remotely to check the contents of any HTML document you edit in Vim and determine if the document is HTML5-conformant (valid).
The filetype plugin is also demo'ed in a screencast tutorial on editing Web applications that Kai has blogged about in a VIM IDE for Web applications posting on his blog (see the blog posting for a link to the video).
All that you need to do to install the Vim filetype plugin is to download the plugin source and save it into
~/.vim/ftplugin/html.vim. To use it to check a document, first do
:make within Vim, then use
:cnext and such to locate the errors (for more details, read the section of the Vim docs that relates to those commands.)
How and why it works
Vim has a set of “quickfix” commands that provide something that many development IDEs also have these days: A way to run a compiler or lint checker or other external tool on the contents of a file you are editing, and then to have any errors returned — along with the line and column numbers of the places in your file where the errors occur — as a list that you can then easily step through or jump through one-by-one and fix. It’s a very powerful feature.
Kai’s HTML filetype plugin provides a way to use Vim’s “quickfix” commands to do conformance checking of HTML5 files. The plugin is dead simple; it’s just two lines:
set makeprg=curl\ -s\ -F\ laxtype=yes\ -F\ parser=html5\
\ -F\ level=error\ -F\ out=gnu\ -F\ [email protected]%\
(Note that I've just wrapped the first line for the purpose of readability in this post.)
makeprg option in the first line tells Vim what “make program” you want to use when checking HTML files. And the
errorformat option in the second line tells Vim the expected format of error messages from that “make program” — so that it can parse the error messages to get the line and column numbers of the places in your file where the errors occur (the meanings of the various parts of the string used in that
errorformat value are: %f, filename; %l, line number; %c, column number; %m, error message).
Interaction with Validator.nu
What Kai’s HTML filetype plugin does it to use as the “make program” the curl command-line HTTP client, and in turn, to have curl send a POST request to Validator.nu. The contents of that POST request are set by the parameters and values specified by the
-F options passed to curl. Essentially what this does is to emulate what would happen if you used the form-based interface at the Validator.nu website to manually set the values of the various form fields in that interface. (Note that wget could be probably used here (with different options) to do the same thing.)
What Validator.nu does in return is to send a response with the list of errors — in a format that allows the list of errors to be easily parsed by tools that have built-in support (like Vim’s “quickfix”) for reading error lists that are in a regular format and doing something with them.
GNU-formatted error output
In this case, since the
out=gnu parameter and value were passed to Validator.nu, the particular format in which Validator.nu returns the error list is the standard GNU error format that’s used by many applications (including that other editor, Emacs). This use case (enabling remote validation and error-evaluation with editing applications) is actually one of the main cases for which Henri added the GNU-formatted error-reporting option to Validator.nu.
Validator.nu + Vim = easy HTML5 conformance checking
The end result is that you get the error information back into Vim in a way that lets you more easily locate and fix the errors.
So setting just two options is all it takes in an editing application like Vim to enable Validator.nu to be used remotely like this (that is, to do integrated HTML5 conformance-checking and error-reporting within the editor). This seems to me to be a pretty good testament (another in a long list) to the utility of the Validator.nu service and to the foresight that’s gone into its design.
It guess it also says a lot about the utility of Vim and the foresight that’s gone into its design — but we all already know how great Vim is, right? 🙂
Posted in Conformance Checking | 5 Comments »