issue2(blockdiag-math ver0.0.2)

block.diag

blockdiag {
    plugin math;
    A[label="", background="math://\RR"];
}

result

WARNING: Fail to convert formula: \RR (reason: b"This is e-pTeX, Version 3.1415926-p3.4-110825-2.6 (utf8.euc) (TeX Live 2013/Debian)\n restricted \\write18 enabled.\nentering extended mode\n(/tmp/tmpnwajb8no/tmprm9egx7f.tex\npLaTeX2e <2006/11/10> (based on LaTeX2e <2011/06/27> patch level 0)\nBabel <3.9h> and hyphenation patterns for 11 languages loaded.\n(/usr/share/texlive/texmf-dist/tex/latex/base/article.cls\nDocument Class: article 2007/10/19 v1.4h Standard LaTeX document class\n(/usr/share/texlive/texmf-dist/tex/latex/base/size12.clo))\n(/usr/share/texlive/texmf-dist/tex/latex/base/inputenc.sty\n(/usr/share/texlive/texmf-dist/tex/latex/ucs/utf8x.def))\n(/usr/share/texlive/texmf-dist/tex/latex/ucs/ucs.sty\n(/usr/share/texlive/texmf-dist/tex/latex/ucs/data/uni-global.def))\n(/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsmath.sty\nFor additional information on amsmath, use the `?' option.\n(/usr/share/texlive/texmf-dist/tex/latex/amsmath/amstext.sty\n(/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsgen.sty))\n(/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsbsy.sty)\n(/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsopn.sty))\n(/usr/share/texlive/texmf-dist/tex/latex/amscls/amsthm.sty)\n(/usr/share/texlive/texmf-dist/tex/latex/amsfonts/amssymb.sty\n(/usr/share/texlive/texmf-dist/tex/latex/amsfonts/amsfonts.sty))\n(/usr/share/texlive/texmf-dist/tex/latex/tools/bm.sty)\nNo file tmprm9egx7f.aux.\n(/usr/share/texlive/texmf-dist/tex/latex/ucs/ucsencs.def)\n(/usr/share/texlive/texmf-dist/tex/latex/amsfonts/umsa.fd)\n(/usr/share/texlive/texmf-dist/tex/latex/amsfonts/umsb.fd)\n! Undefined control sequence.\n<recently read> \\RR \n                    \nl.11 {\\Huge $\\RR\n                $}\n[1] (./tmprm9egx7f.aux) )\n(see the transcript file for additional information)\nOutput written on tmprm9egx7f.dvi (1 page, 152 bytes).\nTranscript written on tmprm9egx7f.log.\n")