The SDL functions word_is() and word_get(). These access and make use of 18
internal arrays of token information relative to the active version of
POV-Ray(povr). The 18 arrays break down into three sets. Namely. Previous
tokens (back to through v3.6) which are out (o prefix); Tokens included in the
current code (i prefix); Lastly, tokens which are new (n prefix) compared to
the prior major release (v3.8 beta 2). See documentation for more detail on
use.

The array names are:

oOptionNames
oFakeByFnctWords
oFnNames
oOddWords
oDirectiveWords
oKeyWords

iKeyWords
iDirectiveWords
iOddWords
iFnNames
iFakeByFnctWords
iOptionNames

nKeyWords
nDirectiveWords
nOddWords
nFnNames
nFakeByFnctWords
nOptionNames

Any string can be checked against the o & i arrays using word_is("TheString").
The return values will be:

-6 ==> former ini file keyword or command line flag.
-5 ==> former, lower case, shipped identifier pretending to be inbuilt feature.
-4 ==> former inbuilt vm function.
-3 ==> pseudo / hidden keyword removed.
-2 ==> former Scene Description Language (SDL) directives.
-1 ==> former Scene Description Language (SDL) keyword.
 0 ==> not now and never a keyword. Good to go.
+1 ==> active Scene Description Language (SDL) keyword.
+2 ==> active Scene Description Language (SDL) directives.
+3 ==> pseudo / hidden keywords active or potentially active on config.
+4 ==> inbuilt vm function declared in functions.inc or cfunctions.inc.
+5 ==> lower case, shipped identifier pretending to be inbuilt feature.
+6 ==> active ini file keyword or command line flag.

cooresponding to the string being found as a token in the following array:

-6 ==> oOptionNames
-5 ==> oFakeByFnctWords
-4 ==> oFnNames
-3 ==> oOddWords
-2 ==> oDirectiveWords
-1 ==> oKeyWords
 0 ==>
+1 ==> iKeyWords
+2 ==> iDirectiveWords
+3 ==> iOddWords
+4 ==> iFnNames
+5 ==> iFakeByFnctWords
+6 ==> iOptionNames

The word_is() function has a back door which allows it to check the size of
all 18 internal arrays of tokens. Specifically when any of the array names is
prefixed by 0 and passed as a string the word_is() function returns the size
of the array. Further, the minimum array size is 1 though some contain a
dummy token of "!#". To get the size of the o,i and n KeyWords arrays we use:

#debug concat("oKeyWords  count --> ",str(word_is("0oKeyWords"),4,0),"\n")
#debug concat("iKeyWords  count --> ",str(word_is("0iKeyWords"),4,0),"\n")
#debug concat("nKeyWords  count --> ",str(word_is("0nKeyWords"),4,0),"\n")

These will return, for example, something like:

oKeyWords  count -->   29
iKeyWords  count -->  514
nKeyWords  count -->   45

Knowing the size we can then, for example, use a for loop to word_get() all the
strings. Or we can look at particular ones with:

#debug concat("oKeyWords   0 --> ",word_get("0oKeyWords",0),"\n")
#debug concat("iKeyWords  99 --> ",word_get("0iKeyWords",99),"\n")
#debug concat("nKeyWords   0 --> ",word_get("0nKeyWords",0),"\n")

These will return, for example, something like:

oKeyWords   0 --> agate_turb
iKeyWords  99 --> cubic_spline
nKeyWords   0 --> amplify

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With respect to testing any particular string it's expected one of the three
following will be the word_is() forms most used.

#declare MyStr = "lockandkey"

#if (word_is(MyStr)=0)
    #debug concat("No usage conflicts for '",MyStr,"'.\n")
#end

//--- or

#if (word_is(MyStr)!=0)
    #debug concat("Usage conflicts exist for '",MyStr,"'.\n")
#end

//--- or

#if (word_is(MyStr)>0)
    #debug concat("'",MyStr,"' is a part of this POV-Ray version.\n")
#end

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The ability to access all the tokens with word_get will hopefully provide
strings that can act as an index into deeper, more complete, documentation.

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There are thoughts toward some near extensions. Perhaps three pattern arrays
in all-patterns, normal-perturbation-patterns and scalar-value-patterns.
Today, it's sometimes easy to lose track of there being two ripple pattern
implementations for example.

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