SVG: dynamic size based on text, merging objects - svg

Question

<div style="float: left; padding: 10px; border: 1px solid;
background: #ccc">random text</div>
Is there a way to achieve something like this in SVG? I mean to have a rectangle and a text and:
a) rectangle's width and height are dynamic, so when I change the text, the rectangle adjust its size
b) when I move the rectangle, the text goes with it
And would it be easier to achieve something like this in <canvas>?
EDIT:
<defs>
<text id="text1" x="90" y="100" style="text-anchor:start;font-size:30px;">
THIS IS MY HEADER</text>
</defs>
<filter x="0" y="0" width="1" height="1" id="background">
<feFlood flood-color="gray"/>
<feComposite in="SourceGraphic"/>
</filter>
<use xlink:href="#text1" fill="black" filter="url(#background)"/>
Erik Dahlström proposed something like this. How to put padding to the background, how to add eg. shadow or border to the rectangle? And, this doesn't work in IE9, so I cannot accept it. I could just use <foreignObject> if there was a support for it in IE.
And I just figured out the answer for b) point of my question. You have to put both elements in the group:
<g>
<rect x="0" y="0" width="100" height="100" fill="red"></rect>
<text x="50" y="50" font-size="14" fill="blue" text-anchor="middle">Hello</text>
</g>
And then you can move the group using transform param:
<g transform="translate(x, y)">
Seems to work correct in every browser.

Answer 1

You can use JavaScript to adjust the box:
<svg xmlns="http:/www.w3.org/2000/svg" onload="init()" height="100" width="200">
<style type="text/css">
rect {
stroke:black;
stroke-width:1;
fill:#ccc;
}
</style>
<script type="text/javascript">
var text, rect
var padding = 10
function init() {
text = document.getElementsByTagName("text")[0]
rect = document.getElementsByTagName("rect")[0]
adjustRect()
}
function adjustRect() {
var bbox = text.getBBox()
rect.setAttribute("x",bbox.x - padding)
rect.setAttribute("y",bbox.y - padding )
rect.setAttribute("width",bbox.width + 2*padding)
rect.setAttribute("height",bbox.height + 2*padding)
}
</script>
<g>
<rect x="0" y="0" width="100" height="100" fill="red"></rect>
<text x="50" y="50" font-size="14" fill="blue" text-anchor="middle">Hello</text>
</g>
</svg>
<div>
<button onclick="text.textContent='Goodbye';adjustRect()">change text</button>
</div>

Answer 2

Use an svg filter to draw the background, that will adapt to the size and position of the text. See this answer for a full example.