Since I work with a team of people in creating a site, we often have a problem with content that has been copied from some source (normally Word) and has extra formatting (span, style etc).

I have noticed a few people posting about this so thought I'd offer a reasonable solution.

While some people have focused on changing how the paste command works in TinyMCE, I believe the valid_elements is the better choice.

The default for this allows pretty much every thing (no js though) and can be easily cutomised in mysite/_config.php

The default is this (and can be found in cms/_config.php):

HtmlEditorConfig::get('cms')->setOptions(array('valid_elements' => "@[id|class|style|title],#a[id|rel|rev|dir|tabindex|accesskey|type|name|href|target|title|class],-strong/-b[class],-em/-i[class],-strike[class],-u[class],#p[id|dir|class|align|style],-ol[class],-ul[class],-li[class],br,img[id|dir|longdesc|usemap|class|src|border|alt=|title|width|height|align],-sub[class],-sup[class],-blockquote[dir|class],-table[border=0|cellspacing|cellpadding|width|height|class|align|summary|dir|id|style],-tr[id|dir|class|rowspan|width|height|align|valign|bgcolor|background|bordercolor|style],tbody[id|class|style],thead[id|class|style],tfoot[id|class|style],#td[id|dir|class|colspan|rowspan|width|height|align|valign|scope|style],-th[id|dir|class|colspan|rowspan|width|height|align|valign|scope|style],caption[id|dir|class],-div[id|dir|class|align|style],-span[class|align|style],-pre[class|align],address[class|align],-h1[id|dir|class|align|style],-h2[id|dir|class|align|style],-h3[id|dir|class|align|style],-h4[id|dir|class|align|style],-h5[id|dir|class|align|style],-h6[id|dir|class|align|style],hr[class],dd[id|class|title|dir],dl[id|class|title|dir],dt[id|class|title|dir],@[id,style,class]")
);

If you wish to disallow all style tags, use this:

HtmlEditorConfig::get('cms')->setOptions(array('valid_elements' => "@[id|class|title],#a[id|rel|rev|dir|tabindex|accesskey|type|name|href|target|title|class],-strong/-b[class],-em/-i[class],-strike[class],-u[class],#p[id|dir|class|align],-ol[class],-ul[class],-li[class],br,img[id|dir|longdesc|usemap|class|src|border|alt=|title|width|height|align],-sub[class],-sup[class],-blockquote[dir|class],-table[border=0|cellspacing|cellpadding|width|height|class|align|summary|dir|id|style],-tr[id|dir|class|rowspan|width|height|align|valign|bgcolor|background|bordercolor|style],tbody[id|class|style],thead[id|class|style],tfoot[id|class|style],#td[id|dir|class|colspan|rowspan|width|height|align|valign|scope|style],-th[id|dir|class|colspan|rowspan|width|height|align|valign|scope|style],caption[id|dir|class],-div[id|dir|class|align|style],-span[class|align|style],-pre[class|align],address[class|align],-h1[id|dir|class|align|style],-h2[id|dir|class|align|style],-h3[id|dir|class|align|style],-h4[id|dir|class|align|style],-h5[id|dir|class|align|style],-h6[id|dir|class|align|style],hr[class],dd[id|class|title|dir],dl[id|class|title|dir],dt[id|class|title|dir],@[id,style,class]")
);

If you wish to disallow all style tags, spans and divs use this:

HtmlEditorConfig::get('cms')->setOptions(array(
	'valid_elements' => "@[id|class|title],#a[id|rel|rev|dir|tabindex|accesskey|type|name|href|target|title|class],-strong/-b[class],-em/-i[class],-strike[class],-u[class],#p[id|class],-ol[class],-ul[class],-li[class],br,img[id|dir|longdesc|usemap|class|src|border|alt=|title|width|height|align],-sub[class],-sup[class],-blockquote[dir|class],-table[border=0|cellspacing|cellpadding|width|height|class|align|summary|dir|id|style],-tr[id|dir|class|rowspan|width|height|align|valign|bgcolor|background|bordercolor|style],tbody[id|class|style],thead[id|class|style],tfoot[id|class|style],#td[id|dir|class|colspan|rowspan|width|height|align|valign|scope|style],-th[id|dir|class|colspan|rowspan|width|height|align|valign|scope|style],caption[id|dir|class],-pre[class|align],address[class|align],-h1[id|dir|class|align|style],-h2[id|dir|class|align|style],-h3[id|dir|class|align|style],-h4[id|dir|class|align|style],-h5[id|dir|class|align|style],-h6[id|dir|class|align|style],hr[class],dd[id|class|title|dir],dl[id|class|title|dir],dt[id|class|title|dir],@[id,style,class]")
);

I use the third and am considering taking out a lot of the table attributes so that they are less of an issue as well.