For example, I can get the same results by the following two ways.   &lt;html&gt;  &lt;head&gt; &lt;style type="text/css"&gt;  p#red{color:red}    /* This is a CSS id selector*/  p.green{color:green}   /* This is a CSS class selector*/  &lt;/style&gt;  &lt;/head&gt;  &lt;body&gt;  &lt;p id="red"&gt;red color&lt;/p&gt; &lt;p class="green"&gt;greencolor &lt;/p&gt;  &lt;/body&gt; &lt;/html&gt;   They both can give me a colored text. But where is the difference between them? Thanks for your answer.
What's the difference between &lt;div class=""&gt; and &lt;div id=""&gt; when it comes to CSS? Is it alright to use &lt;div id=""&gt;?  I see different developers doing this in both ways, and since I'm self taught, I've never really figured it out.
I sometimes browse erotic media files but I would like to avoid having them appear in files &amp; folders / recent. How can I do that?  The old "making .recently-used.xbel a folder" trick from 10.10 and older doesn't work any more.   Plus I'd prefer to turn off tracking only temporarily.  I also prefer not to use a separate user for this, as switching users sometimes isn't fast enough. Proper submodules of Noetherian modules are intersections of indecomposable modules If $M$ is Noetherian, any submodule $N \neq M$ can be written as a finite intersection of intersection-indecomposable ones.   I just don't know how to begin with the proof of this proposition.   Very kind of you for reading or answering. Question title overlap in new design when title is longer Today I noticed that in new design view count is getting overlapped with question title on scifi.se for longer title:    But it's not site specific as same problem happen in Beta site too ( Hinduism.se):    That's why asked in main meta. How to decide whether missing values are MAR, MCAR, or MNAR I have a large proteomics dataset. In the rows I have the proteins , and in the rows I have the samples.The dataset contains a lot of missing values.  I would like to know I can find out whether missing values are MAR, MCAR, or MNAR, and how I can decide the best imputation technique. Kind regards. The optical density of a medium is quantified by its refractive index $n$. Does it have any correlation with the mass/number density of the medium? In other words is an optically denser medium must have a greater mass density compared to an optically rarer medium? I think I have managed to work this out, however there is no solution provided with the question so I thought it best to check.   My working:  Let $(x,y) \in (A \times B) \cup (C \times D)$  $\Rightarrow x \in (A$ or $C)$ and $y \in (B$ or $D)$  $\Rightarrow (x, y) \in (A \cup C) \times (B \cup D)$  $\Rightarrow (A \times B) \cup (C \times D) \subseteq (A \cup C) \times (B \cup D)$  Now let $(x,y) \in (A \cup C) \times (B \cup D)$  $\Rightarrow x \in (A$ or $C) $ and $y \in (B$ or $D)$  $\Rightarrow (x, y ) \in (A \times B) \cup (A \times D) \cup (C \times B) \cup (C \times D)$  $\Rightarrow (A \cup C) \times (B \cup D) \nsubseteq (A \times B) \cup (C \times D)$  $\Rightarrow (A \times B) \cup (C \times D) \not= (A \cup C) \times (B \cup D)$  Is this correct?  Thank you. css background color with floating elements Is it advisable to use lead-free PCB and solder paste on a first SMD assembly job? Maximum and Minimum values for ints Rstudio is duplicating commands in the command line Do I cast the result of malloc? In , someone suggested in a  that I should not cast the result of malloc. i.e., I should do this: int *sieve = malloc(sizeof(int) * length);  rather than: int *sieve = (int *) malloc(sizeof(int) * length);  Why would this be the case? I've noticed that man pages and other documents formatted by Unix utilities often use double backticks `` followed by double single quotes '' to wrap quoted phrases instead of the double quote character ". Single quotes are similarly replaced. Why is this?  Here are a couple examples, from the man page for grep:   To find all occurrences of the pattern `.Pp' at the beginning of a line:         $ grep '^\.Pp' myfile   The apostrophes ensure the entire expression is evaluated by grep instead  of by the user's shell.  The caret `^' matches the null string at the  beginning of a line, and the `\' escapes the `.', which would otherwise match  any character.   The grep utility is compliant with the IEEE Std 1003.1-2008 (``POSIX.1'')  specification. Why do the $n \times n$ non-singular matrices form an "open" set? Why is the set of $n\times n$ real, non-singular matrices an  open subset of the set of all $n\times n$ real matrices? I don't quite understand what "open" means in this context.  Thank you. Can someone explained, as detailed as possible, the differences between the following types?  List List&lt;Object&gt; List&lt;?&gt;   Let me make this more specific. When would I want to use  // 1  public void CanYouGiveMeAnAnswer(List l) { }  // 2 public void CanYouGiveMeAnAnswer(List&lt;Object&gt; l) { }  // 3 public void CanYouGiveMeAnAnswer(List&lt;?&gt; l) { } Sometimes a suggested edit is  because of a concurrent direct edit that takes precedence.  Since this is no fault of the edit suggestor, such rejections should not count against the suggestor when counting .  Here are some examples where it happened: Do you have tips or a guide how to install Ubuntu in Microsoft Virtual PC?  I have found some (older) information, but I wonder if this is still valid. And it looks very "unfriendly". "All I need (is/are) cigarettes and alcohol": which one is correct? In one of Oasis's songs — Cigarettes and Alcohol — there are two sentences that make me confused:     All I found was cigarettes and alcohol   ...and...     All I need is cigarettes and alcohol   Why would is and was be correct in these sentences instead of are and were, since they're referring to more than one thing? Why does my item name not show up in 1.13? I am in 1.13 Pre-Release 7 trying to make a one command creation and I need an item with a specific name. The command I use is /give @p diamond_sword{display:{Name:"Sword of Power"}} and it gives my a diamond sword, but it doesn't have the name.   This is me running the command.   This is the command not working. Determiners: anyone versus someone I have a website that sells music artists posters. Each artists has a page containing a small bio, and a list of posters we are selling representing the artist.  Currently our HTML looks like that  &lt;h1&gt;{Artist name}&lt;/h1&gt; bio &lt;h2&gt;Posters&lt;/h2&gt; &lt;ul&gt;   &lt;li class="poster"&gt;...&lt;/li&gt;   ... &lt;/ul&gt;   We are redesigning this page, and we have a new template that we really like. Problem is that in this new version the &lt;h2&gt;Posters&lt;/h2&gt; does not appear anywhere on the page.  As you might expect, a significant part of our traffic comes from people typing something like : "{Artist name} poster" on Google.  I fear that, by removing the word "poster" from the page, we will reduce our chances of getting these people to come to the site, since Google might down rank us.  I see several options here :   Give Google a slightly altered page that contains the H2 tags. But I think this falls into the "Black Hat SEO" category. And I don't want that. Put the heading. Hide it with CSS. Everyone wins, including accessibility tools which can determine the structure of the page using the "invisible" heading. But I do not know if this is considered a good practice. Forget about the heading, and find other ways to tell Google that we really are about posters. (via keywords, but do they really have the same "weight" as an H2?) Adapt the design to our SEO need, and find a way to put that heading nicely.   Are there webmasters out there that have been facing the same issue, how did you resolve it?