如何在命名空间中声明森林选项而不使森林树变得混乱？

Question

我安装了森林2016/03/04 v2.0.2。我适应了我如何使用森林或其他东西来排版命题逻辑公式的解析树？满足我的需求，得到以下代码。以下代码引入了两个全局选项，wff和connective。

\documentclass[convert={size=640}]{standalone}
\usepackage{microtype}
\usepackage[T1]{fontenc}
% forest
\usepackage{forest}
% parsing tree
\forestset{
  declare toks={wff}{},
  declare toks={connective}{},
  parsing tree/.style={
    declare dimen register={parsing tree sep},
    parsing tree sep=5pt,
    % Append the current root to a new phantom root.
    for root'={
      replace by={[,phantom,append=!last dynamic node]}
    },
    % `for tree` applies only to the subtree of the new phantom root.
    for tree={
      math content,
      parent anchor=children,
      child anchor=parent,
      inner sep=0pt,
      if n children=1{!first.calign with current edge}{},
      delay={
        content=\circ,
        insert before/.wrap pgfmath arg={
          [##1,no edge,math content,anchor=base east,
          before computing xy={
            s/.pgfmath={s("!n")-\forestregister{parsing tree sep}}
          }]
        }{wff},
        if connective={}{connective/.option=wff}{},
        insert after/.wrap pgfmath arg={
          [##1,no edge,math content,anchor=base west,
          before computing xy={
            s/.pgfmath={s("!p")+\forestregister{parsing tree sep}}
          }]
        }{connective},
      }
    }
  }
}
\begin{document}
\begin{forest}
  parsing tree
  [,wff=p_0\wedge q_0,connective=\wedge
  [,wff=p_0] [,wff=q_0 []]]
\end{forest}
\end{document}

我不喜欢它declare toks={option}{}扰乱全局命名空间。我只想定义parsing tree样式选项。如何将选项放在安全命名空间内，而不会使森林树木变得杂乱？