This is a primer for producing documents in HTML, the markup language used by the World Wide Web.
This primer assumes that you have:
HTML documents are in plain (also known as ASCII) text format and can be created using any text editor (e.g., Emacs or vi on UNIX machines). A couple of Web browsers (tkWWW for X Window System machines and CERN's Web browser for NeXT computers) include rudimentary HTML editors in a WYSIWYG environment. There are also some WYSIWIG editors available now (e.g. HotMetal for Sun Sparcstations, HTML Edit for Macintoshes). You may wish to try one of them first before delving into the details of HTML.
You can preview a document in progress with NCSA Mosaic (and some other Web browsers). Open it with the Open Local command under the File menu.After you edit the source HTML file, save the changes. Return to NCSA Mosaic and Reload the document. The changes are reflected in the on-screen display.
Here is a bare-bones example of HTML:
<TITLE>The simplest HTML example</TITLE>
<H1>This is a level-one heading</H1>
Welcome to the world of HTML.
This is one paragraph.<P>
And this is a second.<P>
Click here to see the formatted version
of the example.
HTML uses markup tags to tell the Web browser how to display the text. The above example uses:
HTML tags consist of a left angle bracket (<), (a ``less than'' symbol to mathematicians), followed by name of the tag and closed by a right angular bracket (>). Tags are usually paired, e.g. <H1> and </H1>. The ending tag looks just like the starting tag except a slash (/) precedes the text within the brackets. In the example, <H1> tells the Web browser to start formatting a level-one heading; </H1> tells the browser that the heading is complete.
The primary exception to the pairing rule is the <P> tag. There is no such thing as </P>.
NOTE: HTML is not case sensitive. <title> is equivalent to <TITLE> or <TiTlE>.
Not all tags are supported by all World Wide Web browsers. If a browser does not support a tag, it just ignores it.
Every HTML document should have a title. A title is generally displayed separately from the document and is used primarily for document identification in other contexts (e.g., a WAIS search). Choose about half a dozen words that describe the document's purpose.
In the X Window System and Microsoft Windows versions of NCSA Mosaic, the Document Title field is at the top of the screen just below the pulldown menus. In NCSA Mosaic for Macintosh, text tagged as <TITLE> appears as the window title.
HTML has six levels of headings, numbered 1 through 6, with 1 being the most prominent. Headings are displayed in larger and/or bolder fonts than normal body text. The first heading in each document should be tagged <H1>. The syntax of the heading tag is:
<Hy>Text of heading </Hy >
where y is a number between 1 and 6 specifying the level of the heading.
For example, the coding for the ``Headings'' section heading above is
<H3>Headings</H3>
In many documents, the first heading is identical to the title. For multipart documents, the text of the first heading should be suitable for a reader who is already browsing related information (e.g., a chapter title), while the title tag should identify the document in a wider context (e.g., include both the book title and the chapter title, although this can sometimes become overly long).
Unlike documents in most word processors, carriage returns in HTML files aren't significant. Word wrapping can occur at any point in your source file, and multiple spaces are collapsed into a single space. (There are couple of exceptions; space following a <P> or <Hy> tag, for example, is ignored.) Notice that in the bare-bones example, the first paragraph is coded as
Welcome to HTML.
This is the first paragraph. <P>
In the source file, there is a line break between the sentences. A Web browser ignores this line break and starts a new paragraph only when it reaches a <P> tag.
Important: You must separate paragraphs with <P>. The browser ignores any indentations or blank lines in the source text. HTML relies almost entirely on the tags for formatting instructions, and without the <P> tags, the document becomes one large paragraph. (The exception is text tagged as ``preformatted,'' which is explained below.) For instance, the following would produce identical output as the first bare-bones HTML example:
<TITLE>The simplest HTML example</TITLE><H1>This is a level
one heading</H1>Welcome to the world of HTML. This is one
paragraph.<P>And this is a second.<P>
However, to preserve readability in HTML files, headings should be on separate lines, and paragraphs should be separated by blank lines (in addition to the <P> tags).
NCSA Mosaic handles <P> by ending the current paragraph and inserting a blank line.
In HTML+, a successor to HTML currently in development, <P> becomes a ``container'' of text, just as the text of a level-one heading is ``contained'' within<H1> ... </H1>:
<P>
This is a paragraph in HTML+.
</P>
The difference is that the </P> closing tag can always be omitted. (That is, if a browser sees a <P>, it knows that there must be an implied </P> to end the previous paragraph.) In other words, in HTML+, <P> is a beginning-of-paragraph marker.
The advantage of this change is that you will be able to specify formatting options for a paragraph. For example, in HTML+, you will be able to center a paragraph by coding
<P ALIGN=CENTER>
This is a centered paragraph. This is HTML+, so you can't do it yet.
This change won't effect any documents you write now, and they will
continue to look just the same with t do used to distribute additional information such as the access policy.
If the variable of the form name = value is
followed by the default keyword, the variable will be
listed as part of the default system variables (ntpq rv
command). These additional variables serve informational purposes only.
They are not related to the protocol other that they can be listed. The
known protocol variables will always override any variables defined via
the setvar mechanism.
sys_var_list holds the
names of all system variables. The peer_var_list holds the
names of all peer variables and the clock_var_list holds
the names of the reference clock variables.
logfile logfile
syslog facility.
logconfig configkeyword
syslog facility or the alternate
logfile log file. By default, all output is turned on. All
configkeyword keywords can be prefixed with
=, + and -, where =
sets the syslogmask, + adds and -
removes messages. syslog messages can be controlled in four
classes (, peer, sys and sync).
Within these classes four types of messages can be controlled.
info) control configuration
information. Event messages (events) control logging of
events (reachability, synchronization, alarm conditions). Statistical
output is controlled with the statistics keyword. The final
message group is the status messages. This describes mainly the
synchronizations status. Configuration keywords are formed by
concatenating the message class with the event class. The
allprefix can be used instead of a message class. A message
class may also be followed by the all keyword to
enable/disable all messages of the respective message class.
logconfig = syncstatus +sysevents
xntpd and the major system events. For a simple reference
server, the following minimum message configuration could be useful:
logconfig = syncall +clockall
Most variables used by the NTP protocol can be examined with the
xntpdc (mode 7 messages) and the ntpq (mode 6
messages). Currently, very few variables can be modified via mode 6
messages. These variables are either created with the
setvar directive or the leap warning bits. The leap warning
bits can be set in the leapwarning variable up to one month
ahead. Both the leapwarning and leapindication
variables have a slightly different encoding than the usual leap bits
interpretation:
00
01/10
11
LEAP_NOWARNING is passed on).