RichTextBox for UWP supports many HTML attribute. The following table lists HTML attributes by name and element and notes whether they are supported by RichTextBox for UWP.
| Name | Elements | Supported |
| abbr | TD, TH | NO |
| accept-charset | FORM | NO |
| accept | FORM, INPUT | NO |
| accesskey | A, AREA, BUTTON, INPUT, LABEL, LEGEND, TEXTAREA | NO |
| action | FORM | NO |
| align | CAPTION | NO |
| align | APPLET, IFRAME, IMG, INPUT, OBJECT | NO |
| align | LEGEND | NO |
| align | TABLE | NO |
| align | HR | NO |
| align | DIV, H1, H2, H3, H4, H5, H6, P | YES |
| align | COL, COLGROUP, TBODY, TD, TFOOT, TH, THEAD, TR | NO |
| alink | BODY | NO |
| alt | APPLET | NO |
| alt | AREA, IMG | NO |
| alt | INPUT | NO |
| archive | APPLET | NO |
| archive | OBJECT | NO |
| axis | TD, TH | NO |
| background | BODY | NO |
| bgcolor | TABLE | YES |
| bgcolor | TR | YES |
| bgcolor | TD, TH | YES |
| bgcolor | BODY | YES |
| border | TABLE | YES |
| border | IMG, OBJECT | YES |
| cellpadding | TABLE | NO |
| cellspacing | TABLE | YES |
| char | COL, COLGROUP, TBODY, TD, TFOOT, TH, THEAD, TR | NO |
| charoff | COL, COLGROUP, TBODY, TD, TFOOT, TH, THEAD, TR | NO |
| charset | A, LINK, SCRIPT | NO |
| checked | INPUT | NO |
| cite | BLOCKQUOTE, Q | NO |
| cite | DEL, INS | NO |
| class | All elements but BASE, BASEFONT, HEAD, HTML, META, PARAM, SCRIPT, STYLE, TITLE | YES |
| classid | OBJECT | NO |
| clear | BR | NO |
| code | APPLET | NO |
| codebase | OBJECT | NO |
| codebase | APPLET | NO |
| codetype | OBJECT | NO |
| color | BASEFONT, FONT | NO |
| cols | FRAMESET | NO |
| cols | TEXTAREA | NO |
| colspan | TD, TH | YES |
| compact | DIR, DL, MENU, OL, UL | NO |
| content | META | NO |
| coords | AREA | NO |
| coords | A | NO |
| data | OBJECT | NO |
| datetime | DEL, INS | NO |
| declare | OBJECT | NO |
| defer | SCRIPT | NO |
| dir | All elements but APPLET, BASE, BASEFONT, BDO, BR, FRAME, FRAMESET, IFRAME, PARAM, SCRIPT | NO |
| dir | BDO | NO |
| disabled | BUTTON, INPUT, OPTGROUP, OPTION, SELECT, TEXTAREA | NO |
| enctype | FORM | NO |
| face | BASEFONT, FONT | YES |
| for | LABEL | NO |
| frame | TABLE | YES |
| frameborder | FRAME, IFRAME | NO |
| headers | TD, TH | NO |
| height | IFRAME | NO |
| height | TD, TH | NO |
| height | IMG, OBJECT | YES |
| height | APPLET | NO |
| href | A, AREA, LINK | YES |
| href | BASE | NO |
| hreflang | A, LINK | NO |
| hspace | APPLET, IMG, OBJECT | YES |
| http-equiv | META | NO |
| id | All elements but BASE, HEAD, HTML, META, SCRIPT, STYLE, TITLE | YES |
| ismap | IMG, INPUT | NO |
| label | OPTION | NO |
| label | OPTGROUP | NO |
| lang | All elements but APPLET, BASE, BASEFONT, BR, FRAME, FRAMESET, IFRAME, PARAM, SCRIPT | NO |
| language | SCRIPT | NO |
| link | BODY | NO |
| longdesc | IMG | NO |
| longdesc | FRAME, IFRAME | NO |
| marginheight | FRAME, IFRAME | NO |
| marginwidth | FRAME, IFRAME | NO |
| maxlength | INPUT | NO |
| media | STYLE | NO |
| media | LINK | NO |
| method | FORM | NO |
| multiple | SELECT | NO |
| name | BUTTON, TEXTAREA | NO |
| name | APPLET | NO |
| name | SELECT | NO |
| name | FORM | NO |
| name | FRAME, IFRAME | NO |
| name | IMG | YES |
| name | A | YES |
| name | INPUT, OBJECT | NO |
| name | MAP | NO |
| name | PARAM | NO |
| name | META | NO |
| nohref | AREA | NO |
| noresize | FRAME | NO |
| noshade | HR | NO |
| nowrap | TD, TH | NO |
| object | APPLET | NO |
| onblur | A, AREA, BUTTON, INPUT, LABEL, SELECT, TEXTAREA | NO |
| onchange | INPUT, SELECT, TEXTAREA | NO |
| onclick |
All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE, TITLE |
NO |
| ondblclick |
All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE, TITLE |
NO |
| onfocus | A, AREA, BUTTON, INPUT, LABEL, SELECT, TEXTAREA | NO |
| onkeydown |
All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE, TITLE |
NO |
| onkeypress |
All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE, TITLE |
NO |
| onkeyup |
All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE, TITLE |
NO |
| onload | FRAMESET | NO |
| onload | BODY | NO |
| onmousedown |
All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE, TITLE |
NO |
| onmousemove |
All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE, TITLE |
NO |
| onmouseout |
All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE, TITLE |
NO |
| onmouseover |
All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE, TITLE |
NO |
| onmouseup |
All elements but APPLET, BASE, BASEFONT, BDO, BR, FONT, FRAME, FRAMESET, HEAD, HTML, IFRAME, ISINDEX, META, PARAM, SCRIPT, STYLE, TITLE |
NO |
| onreset | FORM | NO |
| onselect | INPUT, TEXTAREA | NO |
| onsubmit | FORM | NO |
| onunload | FRAMESET | NO |
| onunload | BODY | NO |
| profile | HEAD | NO |
| prompt | ISINDEX | NO |
| readonly | TEXTAREA | NO |
| readonly | INPUT | NO |
| rel | A, LINK | NO |
| rev | A, LINK | NO |
| rows | FRAMESET | NO |
| rows | TEXTAREA | NO |
| rowspan | TD, TH | YES |
| rules | TABLE | YES |
| scheme | META | NO |
| scope | TD, TH | NO |
| scrolling | FRAME, IFRAME | NO |
| selected | OPTION | NO |
| shape | AREA | NO |
| shape | A | NO |
| size | HR | NO |
| size | FONT | NO |
| size | INPUT | NO |
| size | BASEFONT | NO |
| size | SELECT | NO |
| span | COL | NO |
| span | COLGROUP | NO |
| src | SCRIPT | NO |
| src | INPUT | NO |
| src | FRAME, IFRAME | NO |
| src | IMG | NO |
| standby | OBJECT | NO |
| start | OL | YES |
| style | All elements but BASE, BASEFONT, HEAD, HTML, META, PARAM, SCRIPT, STYLE, TITLE | YES |
| summary | TABLE | NO |
| tabindex | A, AREA, BUTTON, INPUT, OBJECT, SELECT, TEXTAREA | NO |
| target | A, AREA, BASE, FORM, LINK | NO |
| text | BODY | NO |
| title | All elements but BASE, BASEFONT, HEAD, HTML, META, PARAM, SCRIPT, TITLE | YES |
| type | A, LINK | NO |
| type | OBJECT | NO |
| type | PARAM | NO |
| type | SCRIPT | NO |
| type | STYLE | NO |
| type | INPUT | NO |
| type | LI | NO |
| type | OL | NO |
| type | UI | NO |
| type | BUTTON | NO |
| usemap | IMG, INPUT, OBJECT | NO |
| valign | COL, COLGROUP, TBODY, TD, TFOOT, TH, THEAD, TR | YES |
| value | INPUT | NO |
| value | OPTION | NO |
| value | PARAM | NO |
| value | BUTTON | NO |
| value | LI | NO |
| valuetype | PARAM | NO |
| version | HTML | NO |
| vlink | BODY | NO |
| vspace | APPLET, IMG, OBJECT | YES |
| width | HR | NO |
| width | IFRAME | NO |
| width | IMG, OBJECT | YES |
| width | TABLE | NO |
| width | TD, TH | NO |
| width | APPLET | NO |
| width | COL | YES |
| width | COLGROUP | NO |
| width | PRE | NO |
