Fix and update documentation on date options

doc/common.m4

@@ -138,7 +138,7 @@ m4_define({{_reportingoptions_}}, {{
 : multiperiod/multicolumn report by year
 
 `-p --period=PERIODEXP`
-: set start date, end date, and/or reporting interval all at once using [period expressions](manual.html#period-expressions) syntax (overrides the flags above)
+: set start date, end date, and/or reporting interval all at once using [period expressions](manual.html#period-expressions) syntax
 
 `--date2`
 : match the secondary date instead (see command help for other effects)

hledger/Hledger/Cli/CliOptions.hs

@@ -141,7 +141,7 @@ reportflags = [
  ,flagNone ["monthly","M"]   (setboolopt "monthly") "multiperiod/multicolumn report by month"
  ,flagNone ["quarterly","Q"] (setboolopt "quarterly") "multiperiod/multicolumn report by quarter"
  ,flagNone ["yearly","Y"]    (setboolopt "yearly") "multiperiod/multicolumn report by year"
- ,flagReq  ["period","p"]    (\s opts -> Right $ setopt "period" s opts) "PERIODEXP" "set start date, end date, and/or report interval all at once (overrides the flags above)"
+ ,flagReq  ["period","p"]    (\s opts -> Right $ setopt "period" s opts) "PERIODEXP" "set start date, end date, and/or report interval all at once"
  ,flagNone ["date2"]         (setboolopt "date2") "match the secondary date instead. See command help for other effects. (--effective, --aux-date also accepted)"  -- see also hiddenflags
 
   -- status/realness/depth/zero filters

hledger/hledger_options.m4.md

@@ -234,8 +234,18 @@ You can specify a start and/or end date using
 [`-p/--period`](#period-expressions) 
 or a [`date:` query](#queries) (described below).
 All of these accept the [smart date](#smart-dates) syntax.
-One important thing to be aware of when specifying end dates: as in Ledger, end dates are exclusive, 
+
-so you need to write the date *after* the last day you want to include.
+Some notes:
+
+- As in Ledger, end dates are exclusive, so you need to write the date *after*
+  the last day you want to include.
+- As noted in [reporting options](#general-options):
+  among start/end dates specified with *options*, the last (i.e. right-most)
+  option takes precedence.
+- The effective report start and end dates are the intersection of the
+  start/end dates from options and that from `date:` queries.
+  That is, `date:2019-01 date:2019 -p'2000 to 2030'` yields January 2019, the
+  smallest common time span.
 
 Examples:
 
@@ -258,7 +268,7 @@ reports into multiple subperiods.  The basic intervals can be
 selected with one of `-D/--daily`, `-W/--weekly`, `-M/--monthly`,
 `-Q/--quarterly`, or `-Y/--yearly`.  More complex intervals may be
 specified with a [period expression](#period-expressions). 
-Report intervals can not be specified with a [query](#queries), currently. 
+Report intervals can not be specified with a [query](#queries).
 
 ## Period expressions