Each Unicode character is one of a large series of characters, a numbered series. Accordingly each Unicode character has its own unique number, which is usually given in hexadecimal format, with a preceding “U+” to indicate the number indicates a Unicode character, rather than being a hex number for some other purpose. Thus “A” is U+0065, “B” is U+0066 and so forth.
The various characters and symbols in Unicode will appear if the font you are typing in contains the characters.
Most browsers and word processors also use font substitution. That means, if the character isn’t in the current font, then the system will search through all your fonts until it finds one containing that character, and will use the glyph for that font.
In a word processors you may have to insert the character using a font that contains that character. Then, you can change the character back to the normal font, and the glyph will stick.
But sometimes font substitution doesn’t work properly. And it seems to be one of those problems that is difficult to debug. People try reinstalling their browser and such. Sometimes that or something else fixes it.
But even if font substitution is working. and a special character appears when you are typing in a forum on your machine, that doesn’t mean that all users of the forum will see your character. They may not have a font on their machine that contains that character.
What you are calling Alt-Code is a method by which you can produce Unicode characters in Microsoft Office. It also works in a few other applications. But it won’t work when you are typing directly into forums, at least not with browsers that I know about.
The Windows operating system also provides a method for typing all characters of your current OEM Windows 8-bit font and your current Windows DOS font. Set the Num Lock key on. Hold down the left Alt-key and while holding it, type the decimal, not the hexadecimal, number of the character you want on the numeric keypad. This will produce the character with that number in your current DOS code page. If you include a preceding keypad 0, this will include the character with that number in your current Windows code page. But you can only type numbers from 0 to 255 or to 0255, as these old-style character sets only have 256 characters (numbered from 0 to 255). If you enter a larger number, the count just wraps, so that 256 produces the same results as 0, 257 produces the same results as 1, 0257 produces the same results as 01, and so forth. See http://www.i18nguy.com/unicode/codepages.html for various code pages, not all available from Windows.
Presuming your Windows code page is 1252, then most of these 256 characters will have the same value as they have in the Unicode character set. This is why many users don’t realize that this default method used by the system is not the same as the Alt-key Unicode method used in Microsoft Office.
The character 卐 is Unicode character U+5350, not U+534O. (Hex digits are 0 1 2 3 4 5 6 8 9 0 A B C E F, and do not include the letter O.) If one translates hex 5350 into decimal one gets 21328. Accordingly, either of the entities 區 or 卐 should work in HTML. The decimal version is used more often, because older browsers often only supported the decimal version.
If you are typing using Microsoft Office, then you use Alt21328, not Alt213228. And use the numeric keypad. Note that in Microsoft Office and some other applications you can also type the hex value (Including U+ if you wish) and then enter Alt-x immediately to change the number to the Unicode character. You can also enter these entities into some forums (including this one), and they will be converted.
UTF-8 is one of the hard-coded forms of Unicode. It is used in web pages because some hardware has problems with the other hard codings. It is also the normal Unicode encoding in Macintosh and Linux systems. Microsoft Windows normally uses UTF16 instead. UTF-32 is full length Unicode, but the increased length of the file when using UTF-32 means that it is seldom used.
The official Unicode character charts are found at http://www.unicode.org/charts/ and http://www.unicode.org/charts/symbols.html .
You can also download and install the free Quick Unicode Input Tool from http://www.cardbox.com/quick.htm . This allows you to enter any base plane characters (that is characters from U+0000 to U+FFFF) by entering either their hexadecimal or decimal values. (To enter the hexadecimal values press left-Alt, while holding it press the dot on the numeric keypad, then while continuing to hold left-alt, type the four digits of the Unicode number on numeric keypad or regular keyboard.) The application Babelmap provides an up-to-date visual way of entering every Unicode value without worrying about searching the character out in a particular font. See http://www.babelstone.co.uk/Software/BabelMap.html .
You may also edit some of the keys combinations on your keyboard to include Unicode characters other than those normally provided. See http://www.microsoft.com/globaldev/tools/msklc.mspx for a free utility from Microsoft. There are other keyboard layout editors that cost, but are also more powerful.
Some are included among the Windows utilities available at http://www.alanwood.net/unicode/utilities.html .