Add the following to menu. This is a pretty common technique for creating margins between items.
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Our submenu is going to look just like the top-level menu, except the whole thing will be nested inside a list item. Change the. This provides a lot of crucial information for search engines.
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It allows Google to see that all these new items are associated with the Features label and that they form an isolated section of our website. You should always mark up complex navigation menus with this kind of structure.
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Add a few lines to the. The submenu is no longer part of the static flow of the page, so our top-level menu items are back to normal. However, the submenu should appear underneath the Features label—not in the corner of the browser window. What a coincidence…we just learned how do that! Turning that into a positioned element should change the coordinate system used by our absolutely positioned. Ok, next problem. Until now, all our HTML elements rendered above or below one another in an intuitive way.
The z-index property lets you control the depth of elements on the page. If you think of your screen as 3D space, negative z-index values go farther into the page, and positive ones come out of the page. In other words, the. The Features label should now appear on top of the submenu. Take note of that position: relative; line. We threw in an example of the cursor property to make it look like a link when the user hovers over the label. You can read more about it at Mozilla Developer Network.
Submenu done! Our final task is to hide it until the user hovers over it. Remember that :hover pseudo-class from the CSS Selectors chapter?
We can use that to turn our submenu into an interactive dropdown. First, we need to change our existing. Update the. Then, we need to initially hide the submenu using the display property.
Add a new rule to menu. Setting display to none makes an element completely disappear. This clever combination of descendant selectors and pseudo-classes enables us to conditionally hide or show an element. Relative positioning was for tweaking the position of an element without affecting its surrounding boxes.
Absolute positioning took elements out of the static flow of the page and placed them relative to the browser window, while relatively absolute positioning allowed us to hook back into the static flow of the page. Finally, fixed positioning let us make elements that didn't scroll with the rest of the page. We used these new positioning techniques to create a rather sophisticated navigation menu. This menu was also a pretty good example of how starting with the HTML markup makes life a lot easier. First, we created the semantic structure we wanted. Then , we wrote some fancy CSS to position the boxes right where we wanted them.
But, we will be able to tackle the latter problem with some responsive design in the next chapter. Positioned Elements. Relative Positioning. Absolute Positioning. Relatively Absolute Positioning. Fixed Positioning. Positioned Elements for Animation. Positioned Elements for Menus. Word boundaries and quantifiers are blue, character classes are orange, and escaped literals are gray.
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You'll see additional colors like green for grouping and purple for meta tokens later in the tutorial. With the above regular expression pattern, you can search through a text file to find email addresses, or verify if a given string looks like an email address. This tutorial uses the term "string" to indicate the text that the regular expression is applied to. This website highlights them in green. The term "string" or "character string" is used by programmers to indicate a sequence of characters.
In practice, you can use regular expressions with whatever data you can access using the application or programming language you are working with. A regular expression "engine" is a piece of software that can process regular expressions, trying to match the pattern to the given string. Usually, the engine is part of a larger application and you do not access the engine directly.
Rather, the application invokes it for you when needed, making sure the right regular expression is applied to the right file or data. As usual in the software world, different regular expression engines are not fully compatible with each other. The syntax and behavior of a particular engine is called a regular expression flavor. The tutorial alerts you when these flavors require different syntax or show different behavior. Even if your application is not explicitly covered by the tutorial, it likely uses a regex flavor that is covered, as most applications are developed using one of the programming environments or regex libraries just mentioned.
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You can easily try the following yourself in a text editor that supports regular expressions, such as EditPad Pro. If you do not have such an editor, you can download the free evaluation version of EditPad Pro to try this out. EditPad Pro's regex engine is fully functional in the demo version. As a quick test, copy and paste the text of this page into EditPad Pro. Then select Search Multiline Search Panel in the menu. In the search panel that appears near the bottom, type in regex in the box labeled "Search Text".
Mark the "Regular expression" checkbox, and click the Find First button. This is the leftmost button on the search panel. See how EditPad Pro's regex engine finds the first match. Click the Find Next button, which sits next to the Find First button, to find further matches. When there are no further matches, the Find Next button's icon flashes briefly.
This regex finds all names, singular and plural, I have used on this page to say "regex". If we only had plain text search, we would have needed 5 searches. With regexes, we need just one search.
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