WEBVTT 0 00:00.870 --> 00:06.810 We're going to be getting into this later, but just know that the question mark, and that equals sign, these... 1 00:06.810 --> 00:11.520 are known as "reserved characters" for URL encoding. Alright, 2 00:11.850 --> 00:12.970 well this is pretty straightforward... 3 00:13.110 --> 00:13.820 so let's move on. 4 00:14.100 --> 00:15.660 Let's get into the more complicated bit... 5 00:16.670 --> 00:23.330 and that is, what is this about? (sound effect: what did you say?) Well, that is a brilliant question, my dear student... 6 00:23.340 --> 00:25.100 and that's what I want to talk about now. 7 00:26.030 --> 00:32.750 Firstly, the Chrome browser knows that it cannot represent theta in the ISO charset... 8 00:33.200 --> 00:38.930 and so it doesn't even try and represented in that character encoding type, because it can't, it doesn't exist. 9 00:39.500 --> 00:41.000 So what does it do then? 10 00:41.510 --> 00:49.730 Well, the default action by this browser, is that it's going to transform the characters - that theta character - 11 00:50.300 --> 00:54.410 into what's known as "numeric character references". 12 00:54.680 --> 01:00.440 And as I mentioned before, other browsers may behave differently, opting to generate question marks... 13 01:00.440 --> 01:04.560 or even to prevent the input being inserted in the URL entirely. 14 01:04.580 --> 01:06.770 It just depends on the browser. 15 01:07.400 --> 01:10.640 I know we're doing a lot of quick cuts here, but this is very, very important. 16 01:10.740 --> 01:16.430 But I just want to mention here that remember in the previous lecture when we defined the accept-charset encoding... 17 01:16.430 --> 01:20.550 type as utf-8? What happened when we used theta in that instance? 18 01:21.350 --> 01:22.040 Well, that's right... 19 01:22.040 --> 01:27.320 in that case, we actually saw that theta character in the URL itself. 20 01:27.830 --> 01:32.270 And the reason is, is that it's a ASCII safe character. 21 01:32.300 --> 01:37.720 And that just meant that the browser didn't have to encode that character into a numerical character 22 01:37.730 --> 01:38.200 reference. 23 01:38.660 --> 01:45.380 And as I mentioned, it's because that theta character could just be encoded directly into the URL in... 24 01:45.380 --> 01:46.850 its correct encoding type. 25 01:47.080 --> 01:52.640 But now that we've specified an encoding type that does not recognize theta, the browser has to make... 26 01:52.640 --> 01:56.110 another plan. It has to do something right? It can't just do nothing. 27 01:56.420 --> 01:57.740 And that's what it's trying to do, 28 01:57.740 --> 02:01.100 and that's why it converts it into a numerical character reference. 29 02:01.670 --> 02:06.500 OK, so this is the first thing you need to realize is that when the character is outside of that encoding... 30 02:06.500 --> 02:13.260 type, this browser, Chrome, will try and convert that character into a numeric character reference. 31 02:14.060 --> 02:18.560 The important thing to know, though, is that the browser would not have to do this if that character 32 02:18.770 --> 02:21.950 was, in fact part of the encoding type we specify. 33 02:22.280 --> 02:26.960 So this is now something else that has to happen because it doesn't fit within the encoding type. 34 02:26.970 --> 02:31.460 It has to convert that character into a numeric character reference. 35 02:31.780 --> 02:32.910 "Well, what does that mean, Clyde?" 36 02:32.980 --> 02:40.760 Well, it means that each value is encoded into this format - an "&", a "#", a "D" and a ";". 37 02:40.760 --> 02:47.740 And that "D" represents the character's decimal codepoint value in the Unicode character set. 38 02:47.750 --> 02:53.420 This is important and this is the distinguishing difference when a character's outside of the encoding 39 02:53.420 --> 02:53.770 type. 40 02:53.990 --> 03:02.000 If the character is in the encoding type, then what's encoded in the URL is the hexadecimal format 41 03:02.000 --> 03:03.780 of that specific character. 42 03:04.010 --> 03:06.760 Here, that doesn't exist because it's not in the encoding type... 43 03:07.160 --> 03:12.710 therefore it has to be converted into a numeric character reference, and that is stored by the browser as a decimal 44 03:12.830 --> 03:14.150 codepoint value. 45 03:14.750 --> 03:19.670 And before we move on, I just want to remind you that there is a difference between numerical character references, 46 03:19.670 --> 03:25.460 which is what the browser is doing now when a character is not within that accept-charset type, and... 47 03:25.460 --> 03:31.520 an external character set a.k.a. the charset. There are differences between the two. Very quickly, a... 48 03:31.520 --> 03:38.930 numerical character reference, or NCR for short, is just a common markup construct for HTML, and they're used in order 49 03:38.930 --> 03:43.310 to represent characters that cannot be URL encoded. 50 03:43.760 --> 03:50.360 And remember in our example here, that theta, that character cannot be URL encoded because 51 03:50.360 --> 03:53.120 it doesn't exist in encoding type that we've specified. 52 03:53.450 --> 03:56.990 That's why this NCR has been the fallback. 53 03:57.970 --> 04:05.870 With an external character set, for example, this is chosen by us, by the web author, by the programmer. 54 04:05.890 --> 04:07.250 And why do we define it? 55 04:07.270 --> 04:13.270 Well, we define it so we have complete control over what characters we want to allow our browser to accept. 56 04:13.720 --> 04:20.830 So, in short, the numerical character reference is a way for browsers to understand what the characters 57 04:20.830 --> 04:23.980 mean. The external characters set, the charset attribute, 58 04:24.250 --> 04:29.050 well, that's just an encoding that you and I can specify to both browsers and servers. 59 04:29.470 --> 04:32.830 So that's key differences between the two. But enough of this already. 60 04:33.160 --> 04:36.070 Let's jump back into why the URL looks like it does. 61 04:36.500 --> 04:38.680 Remember, we've got this format right. 62 04:39.010 --> 04:46.990 This is the numerical character reference format. And that "D" stores whatever value you are dealing with... 63 04:47.560 --> 04:49.240 in the decimal codepoint value. 64 04:49.450 --> 04:51.520 So what is the theta value? 65 04:52.450 --> 04:57.310 Well, the theta sign has a value of 952 in the browser's numerical character set. 66 04:58.150 --> 05:00.790 This is going to result in what URL? 67 05:00.790 --> 05:04.840 Just take our URL, that standard & # D and ;... 68 05:05.200 --> 05:07.260 and now we can replace the D, right. 69 05:07.310 --> 05:12.280 We can replace that D with the value of 952. There we go, 70 05:12.310 --> 05:13.330 this is what it looks like. 71 05:13.990 --> 05:17.170 Okay, but this doesn't look like our URL previously, does it? 72 05:17.230 --> 05:19.540 We don't have all this weird percentage signs and numbers. 73 05:19.810 --> 05:20.350 That's right. 74 05:20.350 --> 05:23.100 We're not quite done yet because up to this point... 75 05:23.560 --> 05:26.790 no URL encoding has taken place. 76 05:27.040 --> 05:29.290 Whaaat? I know it sounds strange... 77 05:29.500 --> 05:33.160 just remember that URL encoding does have to take place at some point. 78 05:33.280 --> 05:38.920 Every time a URL is sent to a server, there are rules that the browser has to abide by. 79 05:39.040 --> 05:44.620 And the major rule there is that all the characters in that URL has to form part of the extended ASCII 80 05:44.620 --> 05:45.370 character set. 81 05:46.150 --> 05:47.360 That's just a bit of FYI. 82 05:47.770 --> 05:49.990 Don't worry, we're going to be talking more about this later. 83 05:50.740 --> 05:53.650 So for now, let's look at our URL. 84 05:53.740 --> 05:58.330 But now we're not concerned about the number 952 are we? We know what that means... 85 05:58.340 --> 06:04.330 we know that that is the numerical character codepoint in the browser for the theta character. 86 06:04.450 --> 06:05.130 Simple enough. 87 06:05.620 --> 06:09.490 Let's now deal with those other characters, the &, #, and the ; ... 88 06:10.300 --> 06:12.490 only now does URL encoding take place, 89 06:12.490 --> 06:13.540 at this point in time. 90 06:13.780 --> 06:20.800 The URL encoding rules specify that all characters have to be converted into the hexadecimal equivalents. 91 06:20.980 --> 06:26.170 And again, I don't want to get into massive detail about how this conversion takes place, but hexadecimal 92 06:26.200 --> 06:30.820 equivalents of the &, # and ;, are the following... 93 06:31.210 --> 06:36.190 let me make this more clear by changing the colors of each so you can see where they have gone and what 94 06:36.190 --> 06:37.600 their hexadecimal values are. 95 06:41.440 --> 06:47.230 Does that make sense? The & is %27, the # is %23 and... 96 06:47.230 --> 06:53.740 that ; is %3B. Whew, I know. We are covering very advanced things, and I hope you are following 97 06:53.740 --> 06:54.100 along. 98 06:54.340 --> 06:58.330 But you know what's weird, is that this doesn't really solve our problem.