Template:Substitution/doc

With middle text but no additional text at the end
produces:

With both middle text and additional text at the end
produces:

With no middle text but some additional text at the end
produces:

TemplateData
{ "description": "Use this template to add a message box to a template's documentation subpage indicating if and how that template  should be substituted.", "params": { "first parameter": { "label": "1", "description": "Inserts any helpful or instructive text in bold font such as 'always' or 'never' between the words 'should' and 'be' in the resulting message box; if no such instruction is desired, this parameter should be entered as a single blank typed space (in this sense, the parameter is required: it must be an instructive word OR it must be a blank typed space—it must NOT be left with no entry",     "type": "string",      "example": "never",      "required": true    },      "second parameter": {      "label": "2",      "description": "This parameter takes any text you add to it and places it at the end of the sentence that the message box generates; it should NOT end in a period",      "type": "string",      "example": "unless older versions cannot be found",      "default": "",      "required": false    }  } }