RELAX NG schema for Schematron
A correct Schematron schema shall be valid with respect to the following Part 2 schema (RELAX NG Compact Syntax).
#        (c) International Organization for Standardization 2005. 
#       Permission to copy in any form is granted for use with conforming 
#       SGML systems and applications as defined in ISO 8879, 
#       provided this notice is included in all copies.

default namespace sch = "http://purl.oclc.org/dsdl/schematron"

namespace local = ""

start = schema

# Element declarations
schema = element schema {
    attribute id { xsd:ID }?, 
    rich, 
    attribute schemaVersion { non-empty-string }?,
    attribute defaultPhase { xsd:IDREF }?,  
    attribute queryBinding { non-empty-string }?,
    (foreign
     & inclusion*
     &  (title?,
       ns*,
       p*,
       let*,
       phase*,
       pattern+,
       p*,
       diagnostics?))
}

active = element active {
    attribute pattern { xsd:IDREF },
    (foreign & (text | dir | emph | span)*)
}

assert = element assert {
    attribute test { exprValue }, 
    attribute flag { flagValue }?,
    attribute id { xsd:ID }?,
    attribute diagnostics { xsd:IDREFS }?, 
    rich,
    linkable,
    (foreign & (text | name | value-of | emph | dir | span)*)
}

diagnostic = element diagnostic {
    attribute id { xsd:ID },
    rich, 
    (foreign & (text | value-of | emph | dir | span)*)
}
  
diagnostics = element diagnostics { 
    foreign & inclusion* & diagnostic* 
}
    
dir = element dir {
    attribute value { "ltr" | "rtl" }?,
    (foreign & text)
}

emph = element emph { text }

extends = element extends {
    attribute rule { xsd:IDREF },
    foreign-empty
}
  
let = element let {
    attribute name { nameValue },
    attribute value { string }
}

name = element name {
    attribute path { pathValue }?,
    foreign-empty
}

ns = element ns {
    attribute uri { uriValue },
    attribute prefix { nameValue },
    foreign-empty
}

p = element p {
    attribute id { xsd:ID }?,
    attribute class { classValue }?,
    attribute icon { uriValue }?,
    (foreign & (text | dir | emph | span)*)
}

param = element param {
    attribute name { nameValue },
    attribute value { non-empty-string }
}  

pattern = element pattern {     
    rich,
    (foreign & inclusion* & 
     ( (attribute abstract { "true" }, attribute id { xsd:ID }, 
             title?, (p*, let*, rule*))
     |  (attribute abstract { "false" }?, attribute id { xsd:ID }?, 
             title?, (p*, let*, rule*))
     | (attribute abstract { "false" }?, attribute is-a { xsd:IDREF }, 
             attribute id { xsd:ID }?, title?, (p*, param*))
     )
    )
}

phase = element phase {
    attribute id { xsd:ID },
    rich, 
    (foreign & inclusion* & (p*, let*, active*))
}

report = element report {
    attribute test { exprValue }, 
    attribute flag { flagValue }?,
    attribute id { xsd:ID }?,
    attribute diagnostics { xsd:IDREFS }?, 
    rich,
    linkable,
    (foreign &  (text | name | value-of | emph | dir | span)*)
} 

rule = element rule { 
    attribute flag { flagValue }?,
    rich,
    linkable,
    (foreign & inclusion* 
     & ((attribute abstract { "true" }, 
            attribute id { xsd:ID }, let*, (assert | report | extends)+)
        | (attribute context { pathValue },
            attribute id { xsd:ID }?, 
           attribute abstract { "false" }?,
           let*, (assert | report | extends)+)))
}

span = element span {
    attribute class { classValue },
    (foreign & text)
}

title = element title { 
    (text | dir)* 
}

value-of = element value-of {
    attribute select { pathValue },
    foreign-empty
}

# common declarations
inclusion = element include {
    attribute href { uriValue }
}

rich = 
    attribute icon { uriValue }?,
    attribute see { uriValue }?,
    attribute fpi { fpiValue }?,
    attribute xml:lang { langValue }?,
    attribute xml:space { "preserve" | "default" }?

linkable = 
    attribute role { roleValue }?,
    attribute subject { pathValue }?

foreign = 
    foreign-attributes, foreign-element*

foreign-empty = 
    foreign-attributes

foreign-attributes = 
    attribute * - (local:* | xml:*) { text }*

foreign-element =  element * - sch:*  {
    (attribute * { text }
     | foreign-element
     | schema
     | text)*
}

# Data types

uriValue = xsd:anyURI
pathValue = string
exprValue = string
fpiValue = string
langValue = xsd:language
roleValue = string  
flagValue = string
nameValue = string  # In the default query language binding, xsd:NCNAME
classValue = string

non-empty-string = xsd:token { minLength = "1" }