RadEditor does not offer this feature, but if more users request it we will implement it.
Currently, you can create your own custom filter that will contains only the desired symbols that you want to convert to their entities:
<telerik:radeditor OnClientLoad="OnClientLoad" runat="server" ID="RadEditor1"></telerik:radeditor>
<script type="text/javascript">
function OnClientLoad(editor, args)
{
editor.get_filtersManager().add(new MyFilter());
}
MyFilter = function()
{
MyFilter.initializeBase(this);
this.set_isDom(false);
this.set_enabled(true);
this.set_name("ConvertCharactersToEntities");
this.set_description("This filter converts reserved characters to their html entity names.");
this.entities = {
'euro': '\u20ac', 'cent': '\u00a2', 'pound': '\u00a3', 'yen': '\u00a5', 'sect': '\u00a7', 'copy': '\u00a9', 'reg': '\u00ae', 'plusmn': '\u00b1', 'ne': '\u2260',
'asymp': '\u2248', 'le': '\u2264', 'ge': '\u2265', 'divide': '\u00f7', 'times': '\u00d7', 'iexcl': '\u00a1', 'curren': '\u00a4', 'brvbar': '\u00a6', 'uml': '\u00a8',
'ordf': '\u00aa', 'trade': '\u2122', 'larr': '\u2190', 'uarr': '\u2191', 'rarr': '\u2192', 'darr': '\u2193', 'harr': '\u2194', 'crarr': '\u21b5', 'lArr': '\u21d0', 'uArr': '\u21d1',
'rArr': '\u21d2', 'dArr': '\u21d3', 'hArr': '\u21d4', 'loz': '\u25ca', 'spades': '\u2660', 'clubs': '\u2663', 'hearts': '\u2665', 'diams': '\u2666', 'forall': '\u2200',
'part': '\u2202', 'exist': '\u2203', 'empty': '\u2205', 'nabla': '\u2207', 'isin': '\u2208', 'notin': '\u2209', 'ni': '\u220b', 'prod': '\u220f', 'sum': '\u2211', 'minus': '\u2212',
'lowast': '\u2217', 'radic': '\u221a', 'prop': '\u221d', 'ang': '\u2220', 'and': '\u2227', 'or': '\u2228', 'cap': '\u2229', 'cup': '\u222a', 'int': '\u222b', 'there4': '\u2234',
'sim': '\u223c', 'cong': '\u2245', 'equiv': '\u2261', 'sub': '\u2282', 'sup': '\u2283', 'nsub': '\u2284', 'sube': '\u2286', 'supe': '\u2287', 'oplus': '\u2295', 'otimes': '\u2297',
'perp': '\u22a5', 'sdot': '\u22c5', 'laquo': '\u00ab', 'not': '\u00ac', 'macr': '\u00af', 'deg': '\u00b0', 'sup2': '\u00b2', 'sup3': '\u00b3', 'acute': '\u00b4', 'micro': '\u00b5',
'para': '\u00b6', 'middot': '\u00b7', 'cedil': '\u00b8', 'sup1': '\u00b9', 'ordm': '\u00ba', 'raquo': '\u00bb', 'frac14': '\u00bc', 'frac12': '\u00bd', 'frac34': '\u00be', 'iquest': '\u00bf',
'Agrave': '\u00c0', 'Aacute': '\u00c1', 'Acirc': '\u00c2', 'Atilde': '\u00c3', 'Auml': '\u00c4', 'Aring': '\u00c5', 'AElig': '\u00c6', 'Ccedil': '\u00c7', 'Egrave': '\u00c8', 'Eacute': '\u00c9',
'Ecirc': '\u00ca', 'Euml': '\u00cb', 'Igrave': '\u00cc', 'Iacute': '\u00cd', 'Icirc': '\u00ce', 'Iuml': '\u00cf', 'ETH': '\u00d0', 'Ntilde': '\u00d1', 'Ograve': '\u00d2', 'Oacute': '\u00d3',
'Ocirc': '\u00d4', 'Otilde': '\u00d5', 'Ouml': '\u00d6', 'Oslash': '\u00d8', 'Ugrave': '\u00d9', 'Uacute': '\u00da', 'Ucirc': '\u00db', 'Uuml': '\u00dc', 'Yacute': '\u00dd', 'THORN': '\u00de',
'szlig': '\u00df', 'agrave': '\u00e0', 'aacute': '\u00e1', 'acirc': '\u00e2', 'atilde': '\u00e3', 'auml': '\u00e4', 'aring': '\u00e5', 'aelig': '\u00e6', 'ccedil': '\u00e7', 'egrave': '\u00e8',
'eacute': '\u00e9', 'ecirc': '\u00ea', 'euml': '\u00eb', 'igrave': '\u00ec', 'iacute': '\u00ed', 'icirc': '\u00ee', 'iuml': '\u00ef', 'eth': '\u00f0', 'ntilde': '\u00f1', 'ograve': '\u00f2',
'oacute': '\u00f3', 'ocirc': '\u00f4', 'otilde': '\u00f5', 'ouml': '\u00f6', 'oslash': '\u00f8', 'ugrave': '\u00f9', 'uacute': '\u00fa', 'ucirc': '\u00fb', 'uuml': '\u00fc', 'yacute': '\u00fd',
'thorn': '\u00fe', 'yuml': '\u00ff', 'fnof': '\u0192', 'Alpha': '\u0391', 'Beta': '\u0392', 'Gamma': '\u0393', 'Delta': '\u0394', 'Epsilon': '\u0395', 'Zeta': '\u0396', 'Eta': '\u0397',
'Theta': '\u0398', 'Iota': '\u0399', 'Kappa': '\u039a', 'Lambda': '\u039b', 'Mu': '\u039c', 'Nu': '\u039d', 'Xi': '\u039e', 'Omicron': '\u039f', 'Pi': '\u03a0', 'Rho': '\u03a1',
'Sigma': '\u03a3', 'Tau': '\u03a4', 'Upsilon': '\u03a5', 'Phi': '\u03a6', 'Chi': '\u03a7', 'Psi': '\u03a8', 'Omega': '\u03a9', 'alpha': '\u03b1', 'beta': '\u03b2', 'gamma': '\u03b3',
'delta': '\u03b4', 'epsilon': '\u03b5', 'zeta': '\u03b6', 'eta': '\u03b7', 'theta': '\u03b8', 'iota': '\u03b9', 'kappa': '\u03ba', 'lambda': '\u03bb', 'mu': '\u03bc', 'nu': '\u03bd',
'xi': '\u03be', 'omicron': '\u03bf', 'pi': '\u03c0', 'rho': '\u03c1', 'sigmaf': '\u03c2', 'sigma': '\u03c3', 'tau': '\u03c4', 'upsilon': '\u03c5', 'phi': '\u03c6', 'chi': '\u03c7', 'psi': '\u03c8',
'omega': '\u03c9', 'thetasym': '\u03d1', 'upsih': '\u03d2', 'piv': '\u03d6', 'bull': '\u2022', 'hellip': '\u2026', 'prime': '\u2032', 'Prime': '\u2033', 'oline': '\u203e', 'frasl': '\u2044',
'weierp': '\u2118', 'image': '\u2111', 'real': '\u211c', 'alefsym': '\u2135', 'lceil': '\u2308', 'rceil': '\u2309', 'lfloor': '\u230a', 'rfloor': '\u230b', 'lang': '\u2329', 'rang': '\u232a',
'OElig': '\u0152', 'oelig': '\u0153', 'Scaron': '\u0160', 'scaron': '\u0161', 'Yuml': '\u0178', 'circ': '\u02c6', 'tilde': '\u02dc', 'ensp': '\u2002', 'emsp': '\u2003', 'thinsp': '\u2009', 'zwnj': '\u200c',
'zwj': '\u200d', 'lrm': '\u200e', 'rlm': '\u200f', 'ndash': '\u2013', 'mdash': '\u2014', 'lsquo': '\u2018', 'rsquo': '\u2019', 'sbquo': '\u201a', 'ldquo': '\u201c', 'rdquo': '\u201d', 'bdquo': '\u201e',
'dagger': '\u2020', 'Dagger': '\u2021', 'permil': '\u2030', 'lsaquo': '\u2039', 'rsaquo': '\u203a'
};
}
MyFilter.prototype =
{
getHtmlContent: function(content)
{
var regExp = this.createRegEx();
var entities = this.entities;
var newContent = content + "";
newContent = newContent.replace(regExp, function(match, offset, fullText)
{
for (var entity in entities)
{
if (entities[entity] == match)
{
return "&" + entity + ";";
}
}
return match;
});
return newContent;
},
createRegEx: function()
{
var str = "[";
var entities = this.entities;
for (var entity in entities)
{
str += entities[entity];
}
str += "]";
return new RegExp(str, "g");
}
}
MyFilter.registerClass('Telerik.Web.UI.Editor.ConvertCharactersToEntities', Telerik.Web.UI.Editor.Filter);
</script>