razor - Self-closing TagHelper merges html markup of sibling element -

i'm litle confused behaviour of taghelper intoduced in asp.net core mvc. following tutorial a working email tag helper have opportunity write self-closing tags. according article purpose should use attbute htmltargetelement. class below demostrated example:

 [htmltargetelement("email", tagstructure = tagstructure.withoutendtag)] public class emailtaghelper : taghelper {     private const string emaildomain = "contoso.com";     public string mailto { get; set; }     public override void process(taghelpercontext context, taghelperoutput output)     {         output.tagname = "a";         var address = mailto + "@" + emaildomain;         output.attributes.setattribute("href", "mailto:" + address);         output.content.setcontent(address);     } } 

the markup in razor view like:

<strong>support:</strong>     <email mail-to="support"/><br /> <strong>marketing:</strong>     <email mail-to="marketing"/> 

but have unexpected output:

<strong>support:</strong> <a href="mailto:support@contoso.com">     <span>another content</span>     <strong>marketing:</strong> </a> <a href="mailto:marketing@contoso.com"></a> 

why first anchor tag contains <span> , <strong> tags content?
without htmltargetelement attribute , closing tags </email> in razor view have correct behaviour.

i ran same example , able produce same problem. when debugging, noticed tagmode of output set selfclosing default. not valid anchor tag. set tag mode anchor starttagandendtag, , output generated expected.

public override void process(taghelpercontext context, taghelperoutput output) {     output.tagname = "a";      // add line code     output.tagmode = tagmode.starttagandendtag;      var address = mailto + "@" + emaildomain;     output.attributes.setattribute("href", "mailto:" + address);     output.content.setcontent(address); } 

this razor:

<strong>support:</strong><email mail-to="support" /><br /> <strong>marketing:</strong><email mail-to="marketing" /> 

produced output:

<strong>support:</strong><a href="mailto:support@contoso.com">support@contoso.com</a><br /> <strong>marketing:</strong><a href="mailto:marketing@contoso.com">marketing@contoso.com</a>