HTML tags and their attributes with form parameter semantics

tag name	attribute name	possible attribute values
input	type	hidden
input	type	text
input	type	search
input	type	url
input	type	email
input	type	datetime
input	type	date
input	type	month
input	type	week
input	type	time
input	type	datetime-local
input	type	number
input	type	range
input	type	color
input	type	checkbox
input	type	radio
input	type	file
input	type	submit
input	type	image
input	type	reset
input	type	button

CSS properties and their values with link semantics

property name	value name
background-image	url
background	url
cursor	url
content	url
list-style	url
list-style-image	url

How do you turn any URL into an absolute URL?

HTML5's working draft provides a clear definition of how to do things that were until no so far ago "word of mouth" or "tricks of the trade" but lacked proper definitions.

On such thing is how to render what is supposed to be a URI into an absolute URL.

Here's the proposal from the HTML 5 draft from 24/11/2008:

The document base URL of a Document is the absolute URL obtained by running these steps:

1. If there is no base element that is both a child of the head element and has an href attribute, then the document base URL is the document's address.
2. Otherwise, let url be the value of the href attribute of the first such element.
3. Resolve the url URL, using the document's address as the base URL (thus, the base href attribute isn't affect by xml:base attributes).
4. The document base URL is the result of the previous step if it was successful; otherwise it is the document's address.

To resolve a URL to an absolute URL the user agent must use the following steps. Resolving a URL can result in an error, in which case the URL is not resolvable.

1. Let url be the URL being resolved.
2. Let document be the Document associated with url.
3. Let encoding be the character encoding of document.
4. If encoding is UTF-16, then change it to UTF-8.
5. Let base be the base URL for url. (This is an absolute URL.)
6. Parse url into its component parts.
7. If parsing url resulted in a component, then replace the matching subtring of url with the string that results from expanding any sequences of percent-encoded octets in that component that are valid UTF-8 sequences into Unicode characters as defined by UTF-8.
   If any percent-encoded octets in that component are not valid UTF-8 sequences, then return an error and abort these steps.
   Apply the IDNA ToASCII algorithm to the matching substring, with both the AllowUnassigned and UseSTD3ASCIIRules flags set. Replace the matching substring with the result of the ToASCII algorithm.
   If ToASCII fails to convert one of the components of the string, e.g. because it is too long or because it contains invalid characters, then return an error and abort these steps. [RFC3490]
8. If parsing url resulted in a component, then replace the matching substring of url with the string that results from applying the following steps to each character other than U+0025 PERCENT SIGN (%) that doesn't match the original production defined in RFC 3986:
   1. Encode the character into a sequence of octets as defined by UTF-8.
   2. Replace the character with the percent-encoded form of those octets. [RFC3986]
   For instance if url was "//example.com/a^b☺c%FFd%z/?e", then the component's substring would be "/a^b☺c%FFd%z/" and the two characters that would have to be escaped would be "^" and "☺". The result after this step was applied would therefore be that url now had the value "//example.com/a%5Eb%E2%98%BAc%FFd%z/?e".
9. If parsing url resulted in a component, then replace the matching substring of url with the string that results from applying the following steps to each character other than U+0025 PERCENT SIGN (%) that doesn't match the original production defined in RFC 3986:
   1. If the character in question cannot be expressed in the encoding encoding, then replace it with a single 0x3F octet (an ASCII question mark) and skip the remaining substeps for this character.
   2. Encode the character into a sequence of octets as defined by the encoding encoding.
   3. Replace the character with the percent-encoded form of those octets. [RFC3986]
10. Apply the algorithm described in RFC 3986 section 5.2 Relative Resolution, using url as the potentially relative URI reference (R), and base as the base URI (Base). [RFC3986]
11. Apply any relevant conformance criteria of RFC 3986 and RFC 3987, returning an error and aborting these steps if appropriate. [RFC3986] [RFC3987]
    For instance, if an absolute URI that would be returned by the above algorithm violates the restrictions specific to its scheme, e.g. a data: URI using the "//" server-based naming authority syntax, then user agents are to treat this as an error instead.
12. Let result be the target URI (T) returned by the Relative Resolution algorithm.
13. If result uses a scheme with a server-based naming authority, replace all U+005C REVERSE SOLIDUS (\) characters in result with U+002F SOLIDUS (/) characters.
14. Return result.

A URL is an absolute URL if resolving it results in the same URL without an error.

HTML tags with attributes that have link semantics

Static analysis of HTML pages for harvesting links in the code should not necessarily focus on href attributes of anchor tags. Here's a short list of attributes that take a URI as a value along with their HTML tag names:

Tag Name	Attribute Name
a	href
img	src
script	src
iframe	src
base	href
form	action
link	href
input	usemap
input	src
head	profile
frame	src
frame	longdesc

What is "to exacebrate?

I'm reading a book and seeing the inflected verb exacebrated and wondered what it means.
Answers.com says:

To increase the severity, violence, or bitterness of; aggravate: a speech that exacerbated racial tensions; a heavy rainfall that exacerbated the flood problems.

Let's see some examples of using this verb in a sentence:

Global Warming to Exacerbate China's Water Crisis

or

Smoking may exacerbate the increased risk of a blood vessel bursting inside the brain (intracerebral stroke) already faced by people with high blood pressure

So we see that its meaning is to make things worse and move severe.

Generate all combinations of letters 'a'-something of length n

Here’s something that I was just asked this morning by a colleague who needed my help. I explained the solution and then wrote the program with the employee and finally we run it together on some possible input values to make sure that it does indeed do what we want. I think that makes a very good interview question. I tried to phrase it as an interview question with a few steps and some room for discussion:

You want to test a program that receives a string as input and a Boolean value (yes/no) as output.

The input string is some combinations of the characters ‘a’-‘e’ or length 4. For example ‘aaaa’ or ‘beed’

How would you test it?

An expected answer: Exhaustive search / brute force

· How would you implement a generator of such strings?

· How would you make sure that you don’t generate the same string more than once?

· How would you make sure that you don’t skip any possible string?

· How would you generalize your solution for some natural number n and any range within ‘a’-‘z’?

· Can you explain how many combinations are expected?

· How would you test your testing program?

· Say that your strings are now over Unicode (note size of character set), what would be the problems with your implementation?

· Suggest a strategy to solve your testing problem.

Here’s a C program that demonstrates a solution and allows testing the solution via the commandline:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>

void getnext(unsigned char * a,int n,unsigned char k) {
int i;
for(i=n-1;i>=0;--i) {
++a[i];
if (a[i]<=k) {
break;
} else {
a[i]='a';
}
}

return;
}



/*
* input:
* n -- number -- length of string
* k -- letter -- maximum value?
*/
int main( int argc,char*argv[] ) {
int n=0;
unsigned char k=0;
int i=0;
unsigned char *a;
int max;

if (argc!=3)
return 1;

n = atoi(argv[1]);
k = argv[2][0];


if (NULL == (a=malloc(sizeof(unsigned char)*n+1))) {
exit (1);
}

a[n]='\0';

for(i=0;i<n;++i) {
a[i]= 'a';
}

max = (int)pow(k-'a'+1,n);
printf("%s\n",a);
for (i=0; i<max-1;i++){
getnext(a,n,k);
printf("%s\n",a);
}

return 0;
}

A step further up to complicate things would be something that I was once asked in an interview myself. Here’s a link to my blog where I wrote the question and a way to solve it. My solution there is in Perl:

http://shlomoyona.blogspot.com/2007/12/interview-question-next-permutation.html

A Computational Introduction to Number Theory and Algebra

There is a new book called "A Computational Introduction to Number Theory and Algebra" by Victor Shoup. The online version is free.

See: http://shoup.net/ntb/?

Nir makes friend with a dog at the park

Aviv in Illanot Forest

The kids at Illanot forest

From left to right:
Nir, Sivan, Yuval, Noa and Aviv

A simple game with surprising mathematical properties

1. Pick a natural number.
2. If the number is odd, then multiply by 3 and add 1.
3. If the number is even, then divide by 2.
4. Repeat from 2 with the result

You get a series of number.

Apparently, all series ever tested end up with the number 1 (you can continue from there, of course).
If you begin a series with 1 you get a loop (get back to the number you started with). Apparently, this is the only loop ever discovered.
As a result all series have a repeating pattern from a certain point on: 4, 2, 1, 4, 2, 1.....

Mathematicians cannot seem to prove that no matter which number is used as the initial number you will end up with 1. They cannot find a counter example either.

Here are some series:

1. 1, 4, 2, 1,...
2. 2, 1, 4, 2, 1,...
3. 3, 10, 5, 16, 8, 4, 2, 1, 4, 2, 1,...
4. 4, 2, 1, 4, 2, 1,...
5. 5, 16, 8, 4, 2, 1, 4, 2, 1,...
6. 6, 3, 10, 5, 16, 8, 4, 2, 1, 4, 2, 1,...
7. 7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1, 4, 2, 1,...
8. 8, 4, 2, 1, 4, 2, 1,...
9. 9, 28, 14, 7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1, 4, 2, 1,...
10. 10, 5, 16, 8, 4, 2, 1, 4, 2, 1,...

Some interesting questions

• If we try an infinitely large number of numbers, what will we get more, jumps up (that is a step for an odd number) or slides down (that is a step for an even number)?
• How does the series of the length of series up to the first number 1 look like? Does this series have some special or surprising property?

Left Leaning Red-Black Trees

http://www.cs.princeton.edu/%7Ers/talks/LLRB/RedBlack.pdf

Sivan and Aviv building a birds-house

The kids in Zichron Ya'akov

Tigers: Maya, Sivan and Aviv

Michal and Nir

Noa, Aviv and Sivan singing during holiday dinner

Sivan as an MD

"Dr." Nir

Aviv in a Judo competition (he won all matches)