CSS - Classes, IDs, and Elements: What's the Difference?
What's the difference between an id and a class?
Wrapped hexagon topology When a square is wrapped at the edges, obtains a torus. Is it possible to do the same for a hexagon?  What is the shape/topology of wrapping a hexagon?     Note: I was just reading this  and came up with this question. I'm a physicist. Find the value of $P(1)$ File Save dialog unreadable I just updated my iMac to Mojave, and am still trying to setup my preferences.  I tried dark mode, but did not like it (half of me apps seem to ignore it anyway).  I switched to light mode, but this too has problems. The File Save dialog shows a list of Directories and existing files, but the latter are very light grey, almost indistinguishable from the background.    I have searched the Preferences menu, but can't seem to find any setting to set normal contrast levels like in High Sierra. How do you minimise hand washing between every step to keep tools clean? Say you cooking beef steak:  You have to unwrap the beef from its packaging, lay it down, get blood on your hands, wash hands, sprinkle salt, wash hands, grind pepper, rub the seasoning into the beef, wash hands, grab the tongs etc..  Is it normal to wash hands after every step or is there a trick to avoid getting all the tools dirty?  If you watch TV, they don't ever wash as much as I do. How do I handle the window close event (user clicking the 'X' button) in a Python Tkinter program? In my family we have a DNA contradiction – two cousins (at about the 4th cousin level) took a Y-DNA test, but did not match and had two completely different haplogroups.   Since then, I have traced living cousins with the same surname – the only ones left living that I am aware of – and I would love to pay to have them tested to see if we can figure out where the non-paternity event (NPE) or other event happened (i.e. this new cousin could help us determine which line the NPE occurred in depending on which cousin he matches).   Does anyone have a sample letter, or know the best way to go about asking a distant cousin for DNA?   I have their address and am planning to write a letter, but I can't imagine receiving such a letter, so I am not quite sure how to ask without scaring them off. Problem with \mkbibdateapalongextra of biblatex-apa I've just seen that the reason of closing is missing in the reviewing page of closing votes.    Is it a temporary error or it's a bug?  EDIT: Seems that only when there are audits the reason is missing.  If I cannot upload image I will make an ASCII art:  Should this question be closed as: ? (less)  ┌────────────┐ ┌─────┐ ┌────┐ ┌────┐                                              │ Leave Open │ │Close│ │Edit│ │Skip│                                              └────────────┘ └─────┘ └────┘ └────┘ Leave Open if this question should not be closed  Close if this question should be closed for any reason; consider leaving an  explanatory comment before voting  Edit if this question could be improved so that it does not need to be closed  Skip if you are not sure and want to go to the next question A ring of a planet has an inner radius of approximately 52,000 km (measured from the center of the planet) and a radial width of 19 km. Use differentials to estimate the area of the ring. (Round your answer to the nearest thousand.)   I hate asking questions where I have nothing to contribute but I have absolutely no Idea on how to approach this question. A step by step solution to this problem which I could apply to similar problems would be greatly appreciated, thanks in advance. More section headings? I am a novice in LaTeX and I have one question.  Can someone tell me what if you want more heading's in LaTeX. Like 5 or 10 or even 15. Is there a package for that? Help me to get command or ansibile Regex to fetch below details I understand the difference between LET and LET* (parallel versus sequential binding), and as a theoretical matter it makes perfect sense.  But is there any case where you've ever actually needed LET?  In all of my Lisp code that I've looked at recently, you could replace every LET with LET* with no change.  Edit: OK, I understand why some guy invented LET*, presumably as a macro, way back when.  My question is, given that LET* exists, is there a reason for LET to stay around?  Have you written any actual Lisp code where a LET* would not work as well as a plain LET?  I don't buy the efficiency argument.  First, recognizing cases where LET* can be compiled into something as efficient as LET just doesn't seem that hard.  Second, there are lots of things in the CL spec that simply don't seem like they were designed around efficiency at all.  (When's the last time you saw a LOOP with type declarations?  Those are so hard to figure out I've never seen them used.)  Before Dick Gabriel's benchmarks of the late 1980's, CL was downright slow.  It looks like this is another case of backwards compatibility: wisely, nobody wanted to risk breaking something as fundamental as LET.  Which was my hunch, but it's comforting to hear that nobody has a stupidly-simple case I was missing where LET made a bunch of things ridiculously easier than LET*. When we canonically quantize the scalar field in QFT, we use a Lorentz invariant integration measure given by $$\widetilde{dk} \equiv \frac{d^3k}{(2\pi)^3 2\omega(\textbf{k})}.$$  How can I show that it is Lorentz invariant? What are the limits on how I can cast, change, and retract votes? What does ;; do in sh? I've been watching a lot of pro replays ever since the SC2 beta came out, and I've noticed that almost always, when Protoss research upgrades, the shields are the last research chosen. Why is that? Seems to me that if anything, shields should be the most important upgrade, as they affect all Protoss units and buildings. Deny access to a webpage using web.config Who uses Dual_EC_DRBG? Recent news articles have suggested that the NSA may be involved in trying to influence the cryptography in public standards or commercially deployed software, to enable the NSA to decrypt the encrypted traffic.  For example, .  The New York Times article specifically mentions a 2006 NIST standard, where two Microsoft engineers later discovered a serious problem in the scheme.  The New York Times article explains how the standard was written by the NSA, who pushed the scheme hard:     Simultaneously, the N.S.A. has been deliberately weakening the international encryption standards adopted by developers. One goal in the agency’s 2013 budget request was to “influence policies, standards and specifications for commercial public key technologies,” the most common encryption method.      Cryptographers have long suspected that the agency planted vulnerabilities in a standard adopted in 2006 by the National Institute of Standards and Technology, the United States’ encryption standards body, and later by the International Organization for Standardization, which has 163 countries as members.      Classified N.S.A. memos appear to confirm that the fatal weakness, discovered by two Microsoft cryptographers in 2007, was engineered by the agency. The N.S.A. wrote the standard and aggressively pushed it on the international group, privately calling the effort “a challenge in finesse.”    After some sleuthing, I'm pretty certain this is a reference to the  pseudorandom number generator scheme described in NIST SP 800-90.  The weakness is that Dual_EC_DRBG appears to contain a backdoor, and anyone who knows the backdoor can totally break the PRNG.  The weakness was first described in  and was subsequently .  As a consequence, there are now good reasons to suspect that Dual_EC_DRBG contains a NSA backdoor, and the NSA might be able to spy on anyone who is using Dual_EC_DRBG.  My questions:   Who uses Dual_EC_DRBG? Do any commercial products use Dual_EC_DRBG? Does anyone use it? Will grammar errors become correct after enough people use them for enough time? Floating point calculations in LaTeX?