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In this hands-on course, James Williamson demonstrates the concepts that form the foundation of Cascading Style Sheets (CSS), including styling text, adding margins and padding, and controlling how images display. The course also explores the tools needed to work with CSS, the differences between embedded and external styles, how to use selectors to target elements, and what to do when styles conflict.
Attribute selectors are one of my favorite selector types. They allow you to target elements based on the elements' attributes and the values of those attributes. While class and ID selectors allow styling based on a single attribute type, attribute selectors allow you to use any attribute you wish, and the syntax is flexible enough to allow you to target styling based on a number of different factors. So let's go ahead and take a look at this extremely powerful capability that CSS gives us. I have the attribute-selectors.htm open, and you can find this in the 02_12 folder.
Now I'm going to go over the structure of our page really quickly. It's a very, very small, short, little page, but there's a lot going on here that I want to talk about before we start targeting these elements. So we start off with an unordered list and inside that, we have individual list items which then contain links. Now it's the links that I want to really pay attention to. Notice the links all have href attributes, resource attributes, which tells the browser where it needs to go, or where the content that it's looking for is located at. And I also have a title attribute that adds to the accessibility of the links and basically describes what's going on with the links themselves.
Notice that one of them is an external link. It goes out to a site called lynda.com-- I think you've probably heard of it--and the title says visit lynda.com. The second one is a local link, so it would be linking in the same folder, and it's called about.htm, so it's just linking to another page, and the title of this one is visit about us. And then finally we have a link to a document. In this case, it would go into a directory called _docs/plan.pdf, and the title of this one is download our annual report. So maybe that's a link to an external resource that you might want people to download and use.
Now, below this unordered list, we have some paragraphs, and we have classes applied to those paragraphs. And if you've never seen this before, this is a way to apply multiple classes to an element. You just add whitespace between them and you can apply as many classes as you want. So our first paragraph has three classes applied to it: red, blue, and green; our second paragraph just has red and green; the third paragraph has red and blue applied to it; and then the fourth paragraph only has the class red applied to it. So class selectors, we've used those before.
We know what those can do for us, and we know that we could target those elements with class selectors, but we can't really filter or target them based on how many or which of those are applied to it. So we're going to see how attribute selectors can allow us to do that as well. So I'm going to go right up to my formatting, about line 26, where I'm going to start adding my attribute selectors. I'm just going to create a blank line there, and I'll just start off with the most basic attribute selector you can use, and that syntax merely targets the presence of an attribute, so let's see how we do that.
So I'm going to type in a, so I'm targeting all of our links, and then for the attribute you use brackets. So I'm just going to go ahead and do an opening and closing left and right bracket, and then inside those I'm going to type in the word title. So what this is going to do for me is it's going to go down to all of my links and it's going to look for which of them have a title attribute applied to it, and in this case they all have one applied. So then I'm going to go ahead and open up our curly brace, and inside that I'm going to do some very simple formatting here. I'm just going to type in color: red.
So I'm going to save that, and I'll preview it in one of my browsers, and I notice that all of the links go ahead and get that styling. The reason this happens is because every single one of them has this title. So if I were to change this one for just a moment and then go back and refresh, you can see that it loses that targeting, and it loses that targeting because it no longer has that title attribute. Okay, well I need that title attribute, so I'm going to undo that and save it again. Now that's the most basic attribute selector you can use, and it just basically looks for the attribute. If it finds it, it applies the styling.
It doesn't matter what the value is. Well, one of the really cool things about attribute selectors is that you can also check for specific values if you'd like. So I can get a lot more specific with this. I'm going to go right back into that selector and after title, I'm going to type in equals. Now, we'll just go ahead and target the one we deleted a second ago. In quotation marks, I'm going to type in visit lynda.com. Now it's really important that you type the case-sensitive spelling. Anything inside the quotation marks you have to get it exactly the same way it is on the page.
So if I save that, test it in my browser, I can see that now the styling only applies to the first link because it's the only one that has that explicit title attribute value. Now we can also further modify our attribute selectors to deal with not only the contents of an attribute, but match different patterns of that content as well. I'm going to just below this selector, and I'm going to start targeting our paragraph. So I'm going to type in p. Once again, I'm going to open and close one of those left and right brackets, and I'm just going to type in class="red," so nothing really new in terms of what we're doing here.
I'm going to go ahead and open up my curly braces, and I'm just going to apply the same styling, color: red. So I'll save this and refresh my browser, and I notice that only the last paragraph is targeted. Now you may have had this thought while looking at the code: hey! How is this different than a class selector? How is that different than just saying p.red? Well, it's not. It's exactly the same actually. So that's one of the interesting things about this. In many ways that's a lot like a class selector; however, it only targeted the last paragraph, and that's because this value must match exactly.
When I go down into my code, I can see that this is the only one indeed that just has red. Well, what if I wanted to target every single one of these that has the red class applied to it, even though these have multiple classes applied to it? How do I do that? Well, again, one of the nice things about attribute selectors is that they allow us to match patterns as well. So here is what I want you to do. Go right back up here and just before the equal sign, I want you to type in a tilde. Now if you've never used a tilde before, hold the Shift key down and just press the key, normally on left of the number one character, and that's your tilde.
So this ~=, this is a pattern matching, and it basically says go ahead and look for a whitespace-separated list that includes this word. So, it's specifically looking for those whitespace characters in between words, so it's looking for any instance of an attribute where multiple values might be used. So if I save this, go back into my browser and test it, now I see all of those paragraphs get that styling because each one of them has that red as one of the single values in the class attribute.
So again, the tilde allows us to go ahead and say, hey! Anytime this attribute, as well as any other attributes, are applied to it, go ahead and style it. Now there is other pattern matching that we can do as well. Let's revisit our link selector and kind of play around with those a little bit. I'm going to go back up to my link tag, and I'm going to change the title attribute to href, so now we're looking at the href attribute. And right before the equals sign I'm a type in a caret character. So, that caret character just above the six, this says go ahead and match any string that begins with a certain value. And in this case, I'm going to change visit lynda.com to http://.
So now what this is doing is it's saying, hey! Find any href attribute--which would be this-- that begins with this literal string. So in essence, this is a way to target any external link, because when you do an absolute link, you're going to be using http, more than likely. Of course, you could also group it with https if you're using external secured links. So if I go ahead and save this and refresh my browser, I can see that once again, the styling is only applied to the top link, because that is the only absolute or external link that we're using.
Now there is more matching that we can do here as well. The same way that this targets the beginning of a string, if instead of the caret, you used the dollar sign--and again, note that whenever we do these things there is no whitespace in here whatsoever. But when we use the dollar sign, instead of looking at the beginning of a string, we're looking at the end of the string. And in this case, I'm going to go ahead and change this to PDF. So now it would look through all your links and find any links that ended with PDF, which would be in this case resource links, and if I save that and test it, notice that again we are targeting the PDF download link.
In the last two cases we've done matching for the beginning of a literal string and the end of a literal string. What if you want to just test for the existence of a word within a literal string? Well, you can do that one as well. So if I highlight in this case and change my attribute to looking for title again and now instead of the care or the dollar sign I use the asterisk or the wildcard symbol, so it's title*= and I'm just going to type in in quotation marks the word visit. So now what that's going to do is it's going to look through any title attribute of the link and it's going to find any literal string that has the value visit inside of it.
And in this case we can see that these two links have visit inside of it, so we're anticipating that it will target those. So if I save this and test it, indeed it targets those first two links. Now it's not looking for that word visit in any one certain location in the literal string; it's looking for it anywhere. So if I go back into my code and I take the word visit and say please visit about us and save it, you can see the styling still works because the word visit is located somewhere within that title.
Now you might be wondering okay, what's the difference between this and this, because aren't both of them sort of matching that word wherever it's found? It is, but in the case of the tilde it's looking for that attribute value in a series of whitespace-separated attributes. For example, when you apply a class and use whitespace, it doesn't look at that as a literal string; it looks that as multiple values being applied. Whereas within the title this whitespace is just seen as part of a larger literal string. So the star, or the wildcard character, targets literal string values, whereas the tilde targets full attribute values that are just separated through whitespace.
It sounds like a minor difference, but it's really not. It actually a pretty large difference. Now you can use this to create all kinds of really cool formulas. For example, if I go back up to this title and change it to href, notice one of the things that I can do here is I can change visit to _docs, and that would look for any link that's looking for a resource within the docs folder. So that could be a Word document, a PDF, an Excel document, anything, it would all match. And if I save this and test it, I can see that indeed the styling is only applied to that particular resource.
So there's a lot that we can do with attribute selectors, and you've got all those different variations or formulations of the attribute selectors that allows you to target really, really specific instances, and you could do all sorts of really cool things. You could, for example, add an icon to all external links to let people know that clicking on them will take you outside of the site. You could add a PDF icon for every PDF that you're asking somebody to download, and they could sort of visualize which links are going to allow them to download a file. So there is all manner of things that you can do to it, and that's not even all of the different variations on attribute selectors.
It's really close. I think it's certainly enough to give you an idea of just how powerful these selectors are. Now support for attribute selectors isn't that great in some of the older browsers, especially when you get down to some of the substring matching versions; some of the really basic ones were supported a good while ago, but some of the substring matching ones, the support for them is still relatively new. So if you're going to use them, make sure you test your pages thoroughly in all the browsers that you're targeting before committing to them. I also recommend checking out the Selectors Level 3 Specification, which you can find here at w3.org/TR/selectors.
It has a whole section on attribute selectors. It's a great way to learn a little bit more about those pattern-matching attribute selectors that we have just covered, take a look at some of the ones that we didn't get to cover, and it's a great reference for you to use when you're writing these attribute selectors for your own sites.
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