w3c icon + 2.0 3.0 3.2 4.0
Netscape icon 1.0 2.0 3.0 4.0  
MSIE icon 1.0 2.0 3.0 4.0  
Mosaic icon 1.0 2.0      
Opera 1.0 2.1 3.0    
WebTV 0.9 1.2      

<hr>

empty
CSS: in-line element
start tagrequired
end tagforbidden
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The HR element specifies that a horizontal rule of some sort (the default being a shaded engraved line) be drawn across the page.

The MSIE 3.0 DTD specifies that the attribute "lang=" be included with this tag. However, there is no logical reason for it to be here. Horizontal rules are written regardless of directionality or character structure and as yet, no provision is made for vertical rules.

align=
deprecated
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Netscape icon 1.1n 2.0 3.0 4.0  
MSIE icon 1.0 2.0 3.0 4.0  
Opera 1.0 2.1 3.0    
WebTV 0.9 1.2      
forces the rule to display relative to the window margins. This is deprecated in favour of Cascading Style Sheets, however, this is a general deprecation and not specific to <hr>.
"left"
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Opera 1.0 2.1 3.0    
WebTV 0.9 1.2      
forces the rule to be flush left.
<hr align="left" size="10" width="200">

"center"
default
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Opera 1.0 2.1 3.0    
WebTV 0.9 1.2      
forces the rule to be centered between the window margins. WebTV defines this as their default state: align="center" .
<hr align="center" size="10" width="200">

"right"
w3c icon + 2.0 3.0 3.2 4.0
MSIE icon 1.0 2.0 3.0 4.0  
Opera 1.0 2.1 3.0    
WebTV 0.9 1.2      
forces the rule flush right.
<hr align="right" size="10" width="200">

class=
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WebTV 0.9 1.2      
clear=
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Opera 1.0 2.1 3.0    
"When there is already a figure or table in the margin, you sometimes want to position another figure below the figure in the margin rather than alongside it. The CLEAR attribute allows you to move down unconditionally:" (w3)

Alternatively, you can decide to place the figure alongside the figure in the margin just so long as there is enough room. The minimum width needed is specified as "## en" where ##="the" number of nutts or ### pixels where ### is the number of pixels.

"left"
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"move down until left margin is clear" (w3)
"right"
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Opera 1.0 2.1 3.0    
"move down until right margin is clear" (w3)
"all"
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Opera 1.0 2.1 3.0    
"move down until both margins are clear" (w3)
"## en"
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"move down until there is at least 40 en units free" (w3)
"### pixels"
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"move down until there is at least 100 pixels free" (w3)
color=
MSIE icon 1.0 2.0 3.0 4.0  
WebTV 0.9 1.2      
adds colour to the rule (IE 3.0)
It must also be noted that in Netscape the rule color is that set by the background colour (BGCOLOR=")" attribute. Netscape does not honour "color=".
Colours with 140 named Netscape colours and 16 named Internet Explorer colours.
This is a complete explanation of colour by: Gernot Metze
<hr align="center" size="10" width="200" color="fuchsia">

"#rrggbb" this is six hexadecimal numbers that stipulates a specific colour from a palette of 32768 colours. The colours are specified in rr= red, gg= green, bb= blue. According to Microsoft, the "#" sign is optional
Colours with 140 named Netscape colours and 16 named Internet Explorer colours.
This is a complete explanation of colour by: Gernot Metze <hr align="center" size="10" width="200" color="555555">

"colorname" in addition to the #rrggbb combination above, specific colours can be specified by name. Supported colours are:
Colours with 140 named Netscape colours and 16 named Internet Explorer colours.
This is a complete explanation of colour by: Gernot Metze
black, maroon, green, olive, navy, purple, teal, gray, silver (silver),
red, lime, yellow, blue, fuchsia, aqua and white (white)

<hr align="center" size="10" width="200" color="aqua">

<hr align="center" size="10" width="200" color="red">

dir= this attribute is not listed with the HTML 4.0 specification.
"ltr"
"rtl"
id=
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WebTV 0.9 1.2      
invertborder
WebTV 0.9 1.2      
a WebTV tag:
"Use the invertborder attribute to draw a horizontal rule that seems raised from the surface of the page. By default, when the invertborder attribute is not set, the horizontal rule is drawn embossed into the surface of the page."
md=
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"Specifies a message digest or cryptographic checksum for the associated graphic specified by the SRC attribute. It is used when you want to be sure that a linked object is indeed the same one that the author intended, and hasn't been modified in any way. For instance, MD="md5:jV2OfH+nnXHU8bnkPAad/mSQlTDZ", which specifies an MD5 checksum encoded as a base64 character string. The MD attribute is generally allowed for all elements which support URI based links." (w3)
noshade
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Opera 1.0 2.1 3.0    
WebTV 0.9 1.2      
this stipulates that the rule should have no shading but should be a solid bar.
<hr align="center" size="10" width="200" noshade>

Note: the noshade attribute is not supported by MSIE 2.0

size=
deprecated
w3c icon + 2.0 3.0 3.2 4.0
Netscape icon 1.1n 2.0 3.0 4.0  
MSIE icon 1.0 2.0 3.0 4.0  
Opera 1.0 2.1 3.0    
WebTV 0.9 1.2      
this lets the author dictate how thick the rule should be.
<hr align="center" size="5" width="200">

"number" this is the number of pixels that should be in the width of the rule.
<hr align="center" size="15" width="200">

src=
w3c icon + 2.0 3.0 3.2 4.0
the source of the image to appear with the header. The only argument is "URL".
<hr src="rule.gif"> (This is not implemented, nor honoured, yet.)
style=
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Netscape icon 1.0 2.0 3.0 4.0  
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WebTV 0.9 1.2      
title=
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width=
deprecated
w3c icon + 2.0 3.0 3.2 4.0
Netscape icon 1.1n 2.0 3.0 4.0  
MSIE icon 1.0 2.0 3.0 4.0  
Opera 1.0 2.1 3.0    
WebTV 0.9 1.2      
this allows the author to dictate how long the rule should be.
<hr align="center" size="10" width="100">

"number"
Opera 1.0 2.1 3.0    
this is the number of pixels that form the length of the line
<hr align="center" size="10" width="300">

"% (percent)"
Opera 1.0 2.1 3.0    
this is a number from 1 to 100 that stipulates how long the rule should be relative to the width of the browser window. It is expressed as "50%".
<hr align="center" size="10" width="50%">