encoding/xml: document new chardata tag
encoding/xml: document new chardata tag

Followup to CL 16047.
For #12963.

Change-Id: I596cd5109b25a4079b966427411860fde8b9b54a
Reviewed-on: https://go-review.googlesource.com/17232
Reviewed-by: David Crawshaw <a2f0bf29257797dd66800b4fbb9945c3e216c004@golang.org>

suncycheng/go,cloudflare/go,vsekhar/elastic-go,vsekhar/elastic-go,linux-on-ibm-z/go,suncycheng/go,codestation/go,fjballest/golang,suncycheng/go,josharian/go,CAFxX/go,ganboing/go-esx,kim-racktop/go,ganboing/go-esx,fjballest/golang,codestation/go,Samurais/go,miolini/go,akutz/go,cloudflare/go,odeke-em/go,golang/go,christopher-henderson/Go,deft-code/go,Cofyc/go,binarycrusader/go,mwhudson/go,akutz/go,deft-code/go,akutz/go,golang/go,goodlang/good,cyberroadie/go,roth1002/go,deft-code/go,theif519/go,vsekhar/elastic-go,theif519/go,Samurais/go,ImJasonH/go,momchil-velikov/go,Endika/go,roth1002/go,Samurais/go,odeke-em/go,vanloswang/go,codestation/go,vanloswang/go,roth1002/go,cyberroadie/go,kim-racktop/go,nawawi/go,polyverse-security/go,codestation/go,goodlang/good,cloudflare/go,ganboing/go-esx,nawawi/go,polyverse-security/go,linux-on-ibm-z/go,sndnvaps/go,derekmarcotte/go,roth1002/go,polyverse-security/go,Samurais/go,kim-racktop/go,josharian/go,miolini/go,codestation/go,ImJasonH/go,linux-on-ibm-z/go,odeke-em/go,deft-code/go,momchil-velikov/go,sndnvaps/go,miolini/go,mwhudson/go,polyverse-security/go,Endika/go,kim-racktop/go,akutz/go,4ad/go,derekmarcotte/go,miolini/go,binarycrusader/go,codestation/go,4ad/go,Cofyc/go,kim-racktop/go,CAFxX/go,Cofyc/go,odeke-em/go,miolini/go,cloudflare/go,cyberroadie/go,deft-code/go,deft-code/go,derekmarcotte/go,cyberroadie/go,theif519/go,vanloswang/go,sndnvaps/go,Endika/go,Endika/go,ganboing/go-esx,vanloswang/go,binarycrusader/go,Endika/go,4ad/go,Cofyc/go,theif519/go,cyberroadie/go,akutz/go,josharian/go,4ad/go,Samurais/go,akutz/go,goodlang/good,CAFxX/go,CAFxX/go,momchil-velikov/go,goodlang/good,vanloswang/go,mwhudson/go,josharian/go,sndnvaps/go,golang/go,derekmarcotte/go,akutz/go,mwhudson/go,fjballest/golang,Cofyc/go,vanloswang/go,4ad/go,binarycrusader/go,deft-code/go,odeke-em/go,Samurais/go,nawawi/go,fjballest/golang,mwhudson/go,ImJasonH/go,suncycheng/go,vsekhar/elastic-go,theif519/go,momchil-velikov/go,vsekhar/elastic-go,Samurais/go,linux-on-ibm-z/go,ganboing/go-esx,CAFxX/go,miolini/go,derekmarcotte/go,ImJasonH/go,polyverse-security/go,miolini/go,Endika/go,mwhudson/go,suncycheng/go,golang/go,ganboing/go-esx,linux-on-ibm-z/go,linux-on-ibm-z/go,theif519/go,goodlang/good,ImJasonH/go,momchil-velikov/go,ImJasonH/go,polyverse-security/go,4ad/go,polyverse-security/go,suncycheng/go,4ad/go,vsekhar/elastic-go,roth1002/go,akutz/go,sndnvaps/go,miolini/go,suncycheng/go,linux-on-ibm-z/go,kim-racktop/go,roth1002/go,ImJasonH/go,binarycrusader/go,linux-on-ibm-z/go,polyverse-security/go,nawawi/go,vanloswang/go,ImJasonH/go,Cofyc/go,odeke-em/go,cyberroadie/go,goodlang/good,goodlang/good,binarycrusader/go,codestation/go,kim-racktop/go,binarycrusader/go,josharian/go,mwhudson/go,odeke-em/go,vsekhar/elastic-go,derekmarcotte/go,golang/go,josharian/go,CAFxX/go,Endika/go,nawawi/go,momchil-velikov/go,nawawi/go,Cofyc/go,goodlang/good,roth1002/go,odeke-em/go,kim-racktop/go,Samurais/go,suncycheng/go,codestation/go,nawawi/go,cyberroadie/go,Cofyc/go,cyberroadie/go,CAFxX/go,fjballest/golang,Endika/go,derekmarcotte/go,cloudflare/go,fjballest/golang,sndnvaps/go,vsekhar/elastic-go,fjballest/golang,cloudflare/go,CAFxX/go,cloudflare/go,theif519/go,binarycrusader/go,ganboing/go-esx,vanloswang/go,golang/go,fjballest/golang,cloudflare/go,theif519/go,momchil-velikov/go,golang/go,golang/go,josharian/go,4ad/go,mwhudson/go,sndnvaps/go,derekmarcotte/go,nawawi/go,ganboing/go-esx,momchil-velikov/go,roth1002/go,sndnvaps/go,josharian/go,deft-code/go