'Render a bem slider html str.
Parameters
subject : str
Subject name.
caption : str
A caption for the bem.
section : str
Name of the section. If section already exists, the bem
will be appended to the end of the section.
decim : int
Use this decimation factor for generating MRI/BEM images
(since it can be time consuming).
n_jobs : int
Number of jobs to run in parallel.
subjects_dir : str | None
Path to the SUBJECTS_DIR. If None, the path is obtained by using
the environment variable SUBJECTS_DIR.
Notes
.. versionadded:: 0.9.0'

def add_bem_to_section(self, subject, caption='BEM', section='bem', decim=2, n_jobs=1, subjects_dir=None):

    caption = ('custom    plot' if (caption == '') else caption)
    html = self._render_bem(subject=subject, subjects_dir=subjects_dir, decim=decim, n_jobs=n_jobs, section=section, caption=caption)
    (html, caption, _) = self._validate_input(html, caption, section)
    sectionvar = self._sectionvars[section]
    self.fnames.append(('%s-#-%s-#-custom' % (caption[0], sectionvar)))
    self._sectionlabels.append(sectionvar)
    self.html.extend(html)
