Setting nxml-child-indent affects nxml-mode

[Richard Lewis]

In extensions/highlight-indentation.el the defvar form:

  (defvar nxml-child-indent nil)

sets a variable which is used by nxml-mode to calculate indents. nxml-mode includes a defcustom form for nxml-child-indent and then uses the integer value of this variable in its nxml-compute-indent-from-previous-line function (amongst others). This function is used by nxml-indent-line which is bound in the nxml-mode-map to TAB. As a result, when python-mode is loaded, hitting TAB in an nxml-mode buffer does not indent the line.

Why does python-mode need to set nxml-child-indent to nil? Would it work to make nxml-child-indent buffer local?