Chapter 4 Intro to HTML

Transcript Chapter 4 Intro to HTML

Chapter 4 Introduction to XHTML

OBJECTIVES

In this chapter, you will learn: • Characteristics of XHTML vs. older HTML.

• How to write XHTML to create web pages: – Controlling document structure – Including images in a document – Inserting hyperlinks for navigation – Making lists and tables – Creating forms for user input – Including meta information for search engines to use © 2010, Robert K. Moniot 2

HTML

• Hyper-Text Markup Language: the foundation of the World-Wide Web • Design goals: – Platform independence: pages can be viewed using a variety of different computers and browsers.

– Universality: servers can store information in their own data formats, but convert it to HTML for access by browsers.

– Convenient linking from one page to another (hypertext).

– HTML conveys the structure of the document, not its precise appearance, allowing for varying display capabilities.

XHTML

• Extensible HTML – Based on HTML, but stricter: must be valid XML – Adds extensibility for future purposes – Improves interoperability with other data formats and user agents • Allows only document's content and structure, not style, to be specified – Formatting is specified with Cascading Style Sheets (CSS) • Designed to facilitate Semantic Web • HTML still accepted by browsers – Use validators to make sure your XHTML is standard – Properly written, XHTML is acceptable to all browsers © 2010, Robert K. Moniot 4

Basic form of XHTML

• An XHTML document is all plain text (no binary formatting codes). The contents can be divided into two categories: – –

Content:

material which the user sees when visiting the page

Meta-information:

information about the document: its structure, formatting, etc.

• Meta-information is distinguished from content by using

tags

. A tag is a tag-name enclosed in angle brackets. Tags usually come in pairs: an

opening tag

and a

closing tag,

which is the same tag-name preceded by a slash.

tag-name

>Content affected by tag<

/tag-name

Nesting of tags

• Opening and closing tags define regions affected by the tags. These regions must

nest

, not

overlap

Yes: < tag1 >Some text < tag2 >more text< /tag2 > and more.< /tag1 > No: < tag1 >Some text < tag2 >more text< /tag1 > and more.< /tag2 >

Rules about Tags

• Not all tags need closing tag – For some tags, a closing tag is

optional

in HTML:

< p >

paragraph. Implies closing of previous paragraph tag.

For these, closing tag mandatory in XHTML.

– For some tags, a closing tag is

never

used:

< br / >

line break. Marks a location, not a region.

For these, XHTML mandates

before closing

• Tag names are case-insensitive in HTML

< br >

and

< BR >

and

< Br >

are all equivalent XHTML mandates lower-case only.

Rules about Tags, cont’d

• Unknown tags are ignored. This rule allows new tags to be introduced into later XHTML standards without causing problems for older browsers. But it also means you need to be careful to spell tag names correctly!

Tags with attributes

• Some tags can be qualified by attributes that provide needed additional information or change the default properties of the tag.

• Attributes are specified within the angle brackets following the opening tag name. (Attributes are never listed in a closing tag.)

tag-name

attribute="value" attribute="value">Content

text<

/tag-name

Tags for Document Type

• These tags were not in original HTML standard: introduced in XHML.

• XML version tag

< ?

xml version="1.0" encoding="utf-8" ?

• Document Type Definition (DTD)

< !DOCTYPE

html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

(These can be cut and pasted from examples on Web. Don’t try to type them in by hand!)

Tags for Document Structure

• Some tags specify the overall structure of the document

< html

> ... <

/html >

encloses the entire document

< head

> ... <

/head >

encloses the

head

portion of the document. Everything in the head portion is meta-information, not content.

< body

> ... <

/body >

encloses the

body

portion of the document. The body portion contains the document's content.

Tags for Document Head

< title >Document title< /title >

- Specifies the title that appears in the title-bar of the browser (

not

in the content area). This tag is optional but should always be included to assist the user in navigating the browser's history list.

< meta

name="keywords" content="word, phrase, etc"

/ >

- Specifies keywords to assist indexing of the page by search engines.

Other head tags will be discussed later.

Tags for Document Body

• Heading tags

< h1 >Main heading< /h1 >

- Formats the enclosed text as a prominent large, bold heading.

< h2 >Sub-heading< /h2 >

- Formats the enclosed text as a large, bold heading but not as prominent as for

< h1 >.

< h3 >Sub-sub heading< /h3 >

- Formats the enclosed text as an even less prominent heading.

... (levels 4 and 5 of decreasing prominence)

< h6 >Minor heading< /h6 >

- Formats the enclosed text as a minor heading, only slightly more prominent than ordinary text.

Organizational Tags

• Paragraphs and Layout

< p >

- start of a new paragraph. The closing

< /p >

tag is optional in HTML but required in XHTML.

< br / >

- line break. Use this where the extra line spacing of a paragraph tag is not desirable, as in an address. Never takes a closing tag.

< center >Centered text< /center >

(deprecated) changes justification of enclosed text (normally left-justified) to centered.

< blockquote >Quoted text< /blockquote >

- for large blocks of quoted material.

< pre >Preformatted text< /pre >

- use this to present a block of text exactly as typed in the document, for instance to show an interactive session with a computer.

Tags for Style

• Explicit style tags

< b >Boldfaced text< /b > < i >Italicized text< /i > < u >Underlined text< /u >

(deprecated)

< tt >Typewriter-font text< /tt >

• Logical style tags

< strong >Prominent text< /strong >

- usually bold

< em >Emphasized text< /em >

- usually italics

< cite >Cited text< /cite >

- usually italicized

< code >Computer code< /code >

Tags for Style

• The

< font >

tag.

– In the early days of web design, this tag was introduced to allow the web programmer to control the font family, typeface, color, etc.

– This tag is now deprecated . Style sheets provide much better control over style and compatibility. However, many web pages still use this tag for simple effects such as text size and color.

Example:

< font size="+1" color="red">Large, red text< /font >

Special characters

• Some characters such as angle brackets are reserved for special meanings in XHTML. Others are not available on many keyboards. These characters can be put into content using codes between ampersand and semicolon:

- the less-than symbol

(left angle bracket)

- the greater-than symbol

(right angle bracket)

- the ampersand sign

& ©

- the copyright symbol

• Many more are defined. Note that unlike tags, these codes

are

case-sensitive in HTML.

Hypertext Links

• Hypertext links connect one document to another. A link has two components: the

link text ,

which the user sees to click on, and the

link target ,

which is the location to which the browser is directed when the link is clicked.

• Form of a hypertext link:

< a href=" target.html

"> link text < /a >

Hypertext Links

• The link target, or href (hypertext reference) is in the form of a

URL:

Uniform Resource Locator.

• A URL has 3 components, not all of which need to be supplied in every reference: – A protocol – An Internet address (either name or IP number) – A file path Example:

http :// www.fordham.edu

/current/index.html

URL protocol

• The protocol portion of a URL specifies the way that the web browser will interact with the server to obtain the resource. Protocols supported by most browsers include:

http

- Hypertext Transport Protocol (the default)

https

- Secure HTTP (used to exchange confidential information such as credit card numbers)

ftp

- File Transfer Protocol, used on some servers that host downloadable materials

file

- for URLs that are files on the same computer where the browser is running

mailto

URL address

• The Internet address portion of a URL can be either a name, e.g. www.fordham.edu

, or a number, e.g. 150.108.13.113

• If omitted, the address of the URL in the href is taken to be the same as the address in the URL of the document containing the link. Thus if the address is omitted from a link in a web page, the link refers to a document on the same server that served that page.

• A URL without an address portion can be either

absolute

relative

, as explained next.

URL file path

• The file path portion of a URL optionally specifies the chain of directories (folders) in which the document is located, and the name of the file itself. The directory names in the chain are separated by slash characters.

• If the file

name

portion of the path is omitted, then it defaults to a value that is defined by the server, typically

index.html

Example: the URL

http :// www.myplace.com

/shopping/fruit/

lacks a file name, and so it might be equivalent to

http :// www.myplace.com

/shopping/fruit/index.html

Relative URLs

• If a URL omits the Internet address portion, then the file path portion can be either

relative

absolute

• An absolute file path begins with a slash; a relative one does not.

• In both cases, the Internet address portion is supplied by that of the referencing document.

• For a relative reference, the chain of directories is also supplied by that of the referencing document.

< a href=" /somepage.html

">Absolute link< /a > < a href=" somepage.html

">Relative link< /a >

Relative URLs

• A relative file path can also specify directories. In this case the chain starts in the same directory as the referencing page.

• Use

../

to indicate the parent directory.

Link referencing a file in a subdirectory of the current page's directory

< a href=" assets/somepage.html

">Relative link< /a >

Link referencing a file in a sibling directory of the current page's directory

< a href=" ../assets/somepage.html

">Relative link< /a >

Absolute URLs

• In an absolute file path, the chain of directories starts at the top of the “URL space” of the server.

Absolute link referencing the top-level home page of a specified server

< a href=" http :// www.somehost.com

">Absolute link< /a >

Absolute link referencing a file in the

shopping

directory of the top level of the web server containing the referencing page

< a href=" /shopping/somepage.html

">Absolute link< /a >

Images

• Use the

< img >

tag to include an image in a page. This tag allows some attributes that specify the size of the image, and alternative text that can be used in place of the image.

• The tag must include a

src

attribute specifying a URL that gives the location of the image.

Example:

< img src="myface.jpg" height="256" width="300" alt="Picture of me" / >

Images

• The image size specification via

length

attributes of the

< img >

and

width

tag can be used to resize the image, but this is not recommended. Rather, the best use of these attributes is to tell the browser how big the image is, so that it can allow the right amount of space in the rendering of the page before it has downloaded the image.

• The alternative text given by

alt

can be displayed by the browser while the image is loading or by browsers that suppress images. Some browsers will pop up a balloon with this text when the mouse hovers over the image. This text can also be read aloud by browsers designed for the blind.

Lists

• List types: –

< ol >

- Ordered list: each item is numbered. Use the

type

attribute

(deprecated)

to obtain letters or roman numerals: the value of the attribute is simply what the item label should look like. Possibilities for

type

are

1, a, A, i, I

–

< ul >

- Unordered list: each item is marked with a bullet.

–

< dl >

- Definition list: the head of each item is a word or phrase, and the rest is a description.

• For

< ol >

and <

ul >

, list items are started by

< li >

(closing tag optional in HTML).

• For

< dl >

, the head word is marked by

< dt >

description by

< dd >

and the (closing tags optional in HTML).

Other XHTML tags

• • • •

Superscripts and subscripts: < sup

>...<

/sup >

< sub

enclose text in >...<

/sub >

tags.

Horizontal rule

(line): use

< hr / >

. It always appears on a line by itself. This tag takes an optional attribute

width

(deprecated)

such as

< hr width="50%“ / >

to control how far across the page it extends.

Strikethrough text:

enclose in

< del

>...<

/del >

tags.

Comments:

these consist of any text enclosed within . Their purpose is to enlighten the web programmer reading the XHTML. They do not appear in the rendered page.

Tables

• The W3C says: “Tables should not be used purely as a means to layout document content as this may present problems when rendering to non-visual media. Additionally, when used with graphics, these tables may force users to scroll horizontally to view a table designed on a system with a larger display. To minimize these problems, authors should use style sheets to control layout rather than tables.

” • Be aware that not all your visitors will use the same hardware or software to view the page.

Defining Tables

• A table organizes content into a grid of horizontal rows and vertical columns.

• The table area is enclosed in

< table > ... < /table >

• A table row is started with

< tr >

(closing tag optional).

• Within each row, a table column item is started with

< td >

(closing tag optional). Use

< th >

instead for column headings.

• Use

align

attribute (values

left

right

center

) to text within a cell.

Table attributes

summary="text" – provides a description of the table's purpose and structure for non-visual agents (e.g. speech) width="length" – specifies width of table.

Length

can be a percentage of the width of the window, or an absolute length in pixels.

Table attributes, cont'd

border="pixels" – specifies width of frame drawn around table. Setting it to 0 suppresses the frame.

cellspacing ="pixels" – specifies spacing between cells (above, below, and to either side) cellpadding ="space" – specifies spacing between the boundary of a cell and its contents. Here

space

can either be a number in pixels, or a percentage of the cell size.

Elements within Table

• Caption: specifies a caption to appear with the table.

– Allows an optional attribute

align

to specify where the caption appears relative to the table. The

align

position

can be one of:

top bottom left right

Cells that Span Rows, Columns

• A single cell can span multiple columns or multiple rows.

• This is achieved using the

rowspan

attributes of the

< th >

< td >

and element.

colspan

Example:

< td colspan="2">This cell spans two columns< /td >

Example:

< td rowspan="2">This cell spans two rows< /td >

You can also use the

nowrap

attribute to control automatic wrapping of text within a cell. Normally wrapping is good in order to prevent a cell from becoming too wide.

Elements within Tables

• Row groups: these allow you to structure portions of the table into head, body, and foot.

< thead

> ... <

/thead >

encloses rows in head of table.

< tfoot

> ... <

/tfoot >

encloses rows in foot of table.

< tbody

> ... <

/tbody >

encloses rows in body of table.

– Note that

< tfoot >

must come before

< tbody >

so that the browser can scroll the body independently of head and foot, or repeat head and foot on multi-page printout.

– Multiple

< tbody >

elements are allowed, in order to divide the body into groups of rows. The browser may put extra space or other indication of the separation between these groups.

– The closing tags are optional in HTML.

Elements within Tables

• Column groups: these allow you to specify width of columns in the table.

Form:

< colgroup > < col

width="width" span="cols"

/ >

...

< /colgroup >

width

can be a number of pixels or a percentage of the table width.

cols

is the number of columns sharing the same attributes.

HTML standard also allows

align

attribute but Firefox ignores it.

Customizing Tables

• Use

colspan

and

rowspan

attributes of

< th >

< td >

to span multiple rows, columns, e.g.

tag

< td colspan="3">Multi-column cell< /td >

• Use

valign

attribute of

< th >

< td >

tag for vertical positioning within cells. Values

top

middle

bottom

• Use

border

attribute of

< table >

tag to show grid lines.

• Use

< caption >

tag inside table to provide a table caption.

Forms

• XHTML forms allow the user to supply data to the web server.

• We will focus on creating the form in XHTML so it appears to the user with input fields and descriptive text, ready to be filled in.

• When the form is submitted, the data entered into the input fields is sent back to the web server and processed, for instance by a CGI program. We will not study CGI programming at this time.

Defining A Form

• A form is defined as follows:

< form

name="form-name" action="path/to/cgi" method="post">

...

(form fields and descriptive text go here)

< /form >

The optional

name

attribute gives the form a name. This is useful when using JavaScript to access the form elements.

The “

path to cgi

” is a URL specifying the location of the CGI program that will process the form. The

method

attribute can be either

"get"

"post"

The region between the opening and closing

< form >

tags can contain input fields and any sort of normal XHTML content.

Form Submit Methods

• Method

"get"

– The input data are appended to the URL of the request sent to the server when the form is submitted. The server passes the data to the CGI through an environment variable.

– This method is primitive and suitable only for very small amounts of form data. It should ordinarily not be used for forms.

• Method

"post"

– The input data are sent to the server in a data body following the request headers. The server passes the data to the CGI through an input mechanism.

– This is the preferred method.

Form Input Fields

• The most common type of form input field is defined using the

< input >

tag, which allows for various types of input elements: text boxes, check boxes, etc. The general form of this tag is

< input

name="field-name" type="input-type" ...

/ >

Note that there is never a closing tag, since this defines an element, not a region.

The

name

attribute gives the input field a name, which is useful for JavaScript and CGI processing. The

type

attribute allows different kinds of input fields to be defined. Depending on the field type, there may be other attributes to control other properties of the element.

Input Field Types

• The

type

attribute can take on one of the following values:

text

- specifies a small box in which the user can type text.

password

- like

text

, but the text which is typed appears as asterisks, though it is submitted to the server as typed.

checkbox

- specifies a box which can be clicked to check or un check it.

radio

specifies a “radio button.” Several buttons of this kind are usually defined as a group, each button of the group having the same name. A radio button is like a checkbox except that only one button of the group can be selected at a time.

Special Input Types

• There are some other input types that are special:

submit

- specifies a Submit button that sends the completed form data to the server.

reset

- specifies a Reset button that restores all input fields of the form to their default initial values.

hidden

- used to provide data that the user does not see.

Other

< input >

Tag Attributes

• • • • size="width" for input fields of type

text password

. The

width

or is an integer giving the width of the box in characters. Default width is 20.

maxlength="length" for fields of type

text password

. Specifies the maximum number of or characters that can be entered into the box.

checked="checked"

buttons (

"checked"

for

checkbox

and

radio

is the only value allowed). If this attribute is present, the choice is selected by default. value="value" specifies a default value for the item or, for submit and reset buttons, a label for the button.

Form Menu Elements

• A menu is defined as follows:

< select

name="name">

< option

> menu item 1

< option

> menu item 2

...

< /select >

Form Menu Elements

• Default appearance of a

select

element has the selected item in a box, with a scroll button at one side that pops up the menu to allow selecting a different item.

• To create a menu that displays several options in the window, include the attribute size="length" where

length

is the number of items to show.

• By default, only one item from the list can be selected. To allow multiple items to be selected, add the attribute

multiple="multiple"

• The

item

tag allows the attribute

selected="selected"

to indicate that the item should be selected by default.

The

textarea

Element

• The

text

type of input element is intended only for small amounts of text. To provide space for more input text, as well as scrollbars, use this element. Example:

< Default text can be placed here.

< textarea /textarea name="remarks" rows="10" cols="25"> >

Anchors

• The

< a >

tag can be used to create an

anchor

, a marked location in a document. The anchor is given an ID using the

attribute. (Other tags can be used too.) • A link can refer to this named location using the

character in the URL. Clicking on the link jumps to the marked location rather than to the top of the referenced document.

Example: Create anchor with

< a id="section1">Section 1.< /a >

Reference anchor with

< a href="#section1">See Section 1.< /a >

Anchors

• The URL referring to an anchor located in the same document can omit everything except the

and the anchor name.

• Or, the URL can be a relative or absolute URL with the

anchorname

at the end.

Example of absolute URL referring to an anchor:

< a href="http://www.mysite.org/pubs/paper.html#section1"> See Section 1 of the paper.< /a >

Chapter 4 Intro to HTML

Transcript Chapter 4 Intro to HTML

Chapter 4

Introduction to XHTML

OBJECTIVES

HTML

XHTML

Basic form of XHTML

Nesting of tags

Rules about Tags

Rules about Tags, cont’d

Tags with attributes

Tags for Document Type

Tags for Document Structure

Tags for Document Head

Tags for Document Body

Organizational Tags

Tags for Style

Tags for Style

Special characters

Hypertext Links

Hypertext Links

URL protocol

URL address

URL file path

Relative URLs

Relative URLs

Absolute URLs

Images

Images

Lists

Other XHTML tags

Tables

Defining Tables

Table attributes

Table attributes, cont'd

Elements within Table

Cells that Span Rows, Columns

Elements within Tables

Elements within Tables

Customizing Tables

Forms

Defining A Form

Form Submit Methods

Form Input Fields

Input Field Types

Special Input Types

Other

< input >

Tag Attributes

Form Menu Elements

Form Menu Elements

The

textarea

Element

Anchors

Anchors

Directory