better explanation and links for err and // +minor fix

docs/appendix-a-index.txt

@@ -250,7 +250,9 @@ quantifier for zero or more findings
 <a id="double-asterisk-op"/>
 **\*\***
 *[«numeric op»](tablet-4-operators.html#numeric-context)* &mdash;
-raises a number to a power, forces numeric context
+raises a number to a power, forces numeric context &mdash;
+example: `2 ** 3` is 8 because its `2 * 2 * 2` &mdash;
+alias to **[exp](#exp)**
 
 <a id="double-asterisk-metachar"/>
 **\*\***
@@ -395,7 +397,7 @@ rational number \([immutable type](appendix-b-grouped.html#immutable-types)
 last created match object of this
 *[block](appendix-g-glossary.html#block)*
 
-<a id="double-slash-op"/>
+<a id="double-slash-op"/><a id="high-err"/>
 **//**
 *[«logical op»](tablet-4-operators.html#logical-selection)* &mdash;
 short circuit *defined or*, returns the first defined value
@@ -431,7 +433,7 @@ example: *`$pair = :key('value')`*
 start of all test methods
 (r w x o R W X O e z s f d l p S b c t u g k T B M A C)
 in the adverbial form &mdash;
-example: *`$filename.IO ~~ :X`*
+example: `$filename.IO ~~ :X`
 
 <a id="colon-twigil"/>
 **:**
@@ -1796,7 +1798,7 @@ contrast with static **[=](#triple-equal)**
 **err** *[«logical op»](tablet-4-operators.html#logical-selection)* &mdash;
 short circuit defined or, returns the first defined value from
 the left, short circuit or,low precedence version of
-**[//](#high-err)**
+**[//](#double-slash-op)**
 
 <a id="ERR-global-var"/>
 **\$\*ERR**
@@ -1866,10 +1868,9 @@ stops all program execution, and returns
 Int $status (first parameter) to the calling environment
 
 <a id="exp"/><a id="exp-op"/>
-**exp** &mdash;
-exponentiate, alias method to: $base (first parameter)
-**[\*\*](#double-asterisk-op)** $exponent (second
-parameter - defaults to e - the euler constant)
+**exp**(Num $base, Num $exp? --> Num) &mdash;
+exponentiate, alias method to: $base **[\*\*](#double-asterisk-op)** $exp
+(defaults to e - the euler constant)
 
 <a id="export"/><a id="export-rouine-trait"/>
 **export**
@@ -2312,10 +2313,12 @@ file handle for thestandard input (command line mostly), see also
 *[«special var»](appendix-b-grouped.html#global-variables)* &mdash;
 include pathes (but not for standard library modules), is @INC in P5
 
+<a id="index"/>
 **index** *(string method)* &mdash;
 finds the first occurrence of a substring in a string
 and returns the numerical position, opposite or **[rindex](#rindex)**
 
+<a id="Inf/>
 **Inf** &mdash;
 indicates infinity, useful to generate infinite lazy
 lists, does in most context same as **[\*](#asterisk)**